Cheat Sheet:

/* *******************************************************************************************
 * SYNOPSIS
 * http://nodejs.org/api/synopsis.html
 * ******************************************************************************************* */


var http = require('http');

// An example of a web server written with Node which responds with 'Hello World'.
// To run the server, put the code into a file called example.js and execute it with the node program.
http.createServer(function (request, response) {
  response.writeHead(200, {'Content-Type': 'text/plain'});
  response.end('Hello World\n');
}).listen(8124);

console.log('Server running at http://127.0.0.1:8124/');


/* *******************************************************************************************
 * GLOBAL OBJECTS
 * http://nodejs.org/api/globals.html
 * ******************************************************************************************* */


// In browsers, the top-level scope is the global scope.
// That means that in browsers if you're in the global scope var something will define a global variable.
// In Node this is different. The top-level scope is not the global scope; var something inside a Node module will be local to that module.

__filename;  // The filename of the code being executed. (absolute path)
__dirname;   // The name of the directory that the currently executing script resides in. (absolute path)
module;      // A reference to the current module. In particular module.exports is used for defining what a module exports and makes available through require().
exports;     // A reference to the module.exports that is shorter to type.
process;     // The process object is a global object and can be accessed from anywhere. It is an instance of EventEmitter.
Buffer;      // The Buffer class is a global type for dealing with binary data directly.


/* *******************************************************************************************
 * CONSOLE
 * http://nodejs.org/api/console.html
 * ******************************************************************************************* */


console.log([data], [...]);             // Prints to stdout with newline.
console.info([data], [...]);            // Same as console.log.
console.error([data], [...]);           // Same as console.log but prints to stderr.
console.warn([data], [...]);            // Same as console.error.
console.dir(obj);                       // Uses util.inspect on obj and prints resulting string to stdout.
console.time(label);                    // Mark a time.
console.timeEnd(label);                 // Finish timer, record output.
console.trace(label);                   // Print a stack trace to stderr of the current position.
console.assert(expression, [message]);  // Same as assert.ok() where if the expression evaluates as false throw an AssertionError with message.


/* *******************************************************************************************
 * TIMERS
 * http://nodejs.org/api/timers.html
 * ******************************************************************************************* */


setTimeout(callback, delay, [arg], [...]);   // To schedule execution of a one-time callback after delay milliseconds. Optionally you can also pass arguments to the callback.
clearTimeout(t);                             // Stop a timer that was previously created with setTimeout().
setInterval(callback, delay, [arg], [...]);  // To schedule the repeated execution of callback every delay milliseconds. Optionally you can also pass arguments to the callback.
clearInterval(t);                            // Stop a timer that was previously created with setInterval().
setImmediate(callback, [arg], [...]);        // To schedule the "immediate" execution of callback after I/O events callbacks and before setTimeout and setInterval.
clearImmediate(immediateObject);             // Stop a timer that was previously created with setImmediate().

unref();  // Allow you to create a timer that is active but if it is the only item left in the event loop, node won't keep the program running.
ref();    // If you had previously unref()d a timer you can call ref() to explicitly request the timer hold the program open.


/* *******************************************************************************************
 * MODULES
 * http://nodejs.org/api/modules.html
 * ******************************************************************************************* */


var module = require('./module.js');    // Loads the module module.js in the same directory.
module.require('./another_module.js');  // load another_module as if require() was called from the module itself.

module.id;        // The identifier for the module. Typically this is the fully resolved filename.
module.filename;  // The fully resolved filename to the module.
module.loaded;    // Whether or not the module is done loading, or is in the process of loading.
module.parent;    // The module that required this one.
module.children;  // The module objects required by this one.

exports.area = function (r) {
  return Math.PI * r * r;
};

// If you want the root of your module's export to be a function (such as a constructor)
// or if you want to export a complete object in one assignment instead of building it one property at a time,
// assign it to module.exports instead of exports.
module.exports = function(width) {
  return {
    area: function() {
      return width * width;
    }
  };
}


/* *******************************************************************************************
 * PROCESS
 * http://nodejs.org/api/process.html
 * ******************************************************************************************* */


process.on('exit', function(code) {});              // Emitted when the process is about to exit
process.on('uncaughtException', function(err) {});  // Emitted when an exception bubbles all the way back to the event loop. (should not be used)

process.stdout;           // A writable stream to stdout.
process.stderr;           // A writable stream to stderr.
process.stdin;            // A readable stream for stdin.

process.argv;             // An array containing the command line arguments.
process.env;              // An object containing the user environment.
process.execPath;         // This is the absolute pathname of the executable that started the process.
process.execArgv;         // This is the set of node-specific command line options from the executable that started the process.

process.arch;             // What processor architecture you're running on: 'arm', 'ia32', or 'x64'.
process.config;           // An Object containing the JavaScript representation of the configure options that were used to compile the current node executable.
process.pid;              // The PID of the process.
process.platform;         // What platform you're running on: 'darwin', 'freebsd', 'linux', 'sunos' or 'win32'.
process.title;            // Getter/setter to set what is displayed in 'ps'.
process.version;          // A compiled-in property that exposes NODE_VERSION.
process.versions;         // A property exposing version strings of node and its dependencies.

process.abort();          // This causes node to emit an abort. This will cause node to exit and generate a core file.
process.chdir(dir);       // Changes the current working directory of the process or throws an exception if that fails.
process.cwd();            // Returns the current working directory of the process.
process.exit([code]);     // Ends the process with the specified code. If omitted, exit uses the 'success' code 0.
process.getgid();         // Gets the group identity of the process.
process.setgid(id);       // Sets the group identity of the process.
process.getuid();         // Gets the user identity of the process.
process.setuid(id);       // Sets the user identity of the process.
process.getgroups();      // Returns an array with the supplementary group IDs.
process.setgroups(grps);  // Sets the supplementary group IDs.

process.initgroups(user, extra_grp);  // Reads /etc/group and initializes the group access list, using all groups of which the user is a member.
process.kill(pid, [signal]);          // Send a signal to a process. pid is the process id and signal is the string describing the signal to send.
process.memoryUsage();                // Returns an object describing the memory usage of the Node process measured in bytes.
process.nextTick(callback);           // On the next loop around the event loop call this callback.
process.maxTickDepth;                 // Callbacks passed to process.nextTick will usually be called at the end of the current flow of execution, and are thus approximately as fast as calling a function synchronously.
process.umask([mask]);                // Sets or reads the process's file mode creation mask.
process.uptime();                     // Number of seconds Node has been running.
process.hrtime();                     // Returns the current high-resolution real time in a [seconds, nanoseconds] tuple Array.


/* *******************************************************************************************
 * CHILD PROCESS
 * http://nodejs.org/api/child_process.html
 * ******************************************************************************************* */


// Node provides a tri-directional popen facility through the child_process module.
// It is possible to stream data through a child's stdin, stdout, and stderr in a fully non-blocking way.

ChildProcess;                                                 // Class. ChildProcess is an EventEmitter.

child.stdin;                                                  // A Writable Stream that represents the child process's stdin
child.stdout;                                                 // A Readable Stream that represents the child process's stdout
child.stderr;                                                 // A Readable Stream that represents the child process's stderr.
child.pid;                                                    // The PID of the child process
child.connected;                                              // If .connected is false, it is no longer possible to send messages
child.kill([signal]);                                         // Send a signal to the child process
child.send(message, [sendHandle]);                            // When using child_process.fork() you can write to the child using child.send(message, [sendHandle]) and messages are received by a 'message' event on the child.
child.disconnect();                                           // Close the IPC channel between parent and child, allowing the child to exit gracefully once there are no other connections keeping it alive.
child_process.spawn(command, [args], [options]);              // Launches a new process with the given command, with command line arguments in args. If omitted, args defaults to an empty Array.
child_process.exec(command, [options], callback);             // Runs a command in a shell and buffers the output.
child_process.execFile(file, [args], [options], [callback]);  // Runs a command in a shell and buffers the output.
child_process.fork(modulePath, [args], [options]);            // This is a special case of the spawn() functionality for spawning Node processes. In addition to having all the methods in a normal ChildProcess instance, the returned object has a communication channel built-in. 


/* *******************************************************************************************
 * UTIL
 * http://nodejs.org/api/util.html
 * ******************************************************************************************* */


// These functions are in the module 'util'. Use require('util') to access them.

util.format(format, [...]);    // Returns a formatted string using the first argument as a printf-like format. (%s, %d, %j)
util.debug(string);            // A synchronous output function. Will block the process and output string immediately to stderr.
util.error([...]);             // Same as util.debug() except this will output all arguments immediately to stderr.
util.puts([...]);              // A synchronous output function. Will block the process and output all arguments to stdout with newlines after each argument.
util.print([...]);             // A synchronous output function. Will block the process, cast each argument to a string then output to stdout. (no newlines)
util.log(string);              // Output with timestamp on stdout.
util.inspect(object, [opts]);  // Return a string representation of object, which is useful for debugging. (options: showHidden, depth, colors, customInspect)
util.isArray(object);          // Returns true if the given "object" is an Array. false otherwise.
util.isRegExp(object);         // Returns true if the given "object" is a RegExp. false otherwise.
util.isDate(object);           // Returns true if the given "object" is a Date. false otherwise.
util.isError(object);          // Returns true if the given "object" is an Error. false otherwise.
util.promisify(fn)             // Takes a function whose last argument is a callback and returns a version that returns promises.

util.inherits(constructor, superConstructor);  // Inherit the prototype methods from one constructor into another.


/* *******************************************************************************************
 * EVENTS
 * http://nodejs.org/api/events.html
 * ******************************************************************************************* */


// All objects which emit events are instances of events.EventEmitter. You can access this module by doing: require("events");
// To access the EventEmitter class, require('events').EventEmitter.
// All EventEmitters emit the event 'newListener' when new listeners are added and 'removeListener' when a listener is removed.

emitter.addListener(event, listener);        // Adds a listener to the end of the listeners array for the specified event.
emitter.on(event, listener);                 // Same as emitter.addListener().
emitter.once(event, listener);               // Adds a one time listener for the event. This listener is invoked only the next time the event is fired, after which it is removed.
emitter.removeListener(event, listener);     // Remove a listener from the listener array for the specified event.
emitter.removeAllListeners([event]);         // Removes all listeners, or those of the specified event.
emitter.setMaxListeners(n);                  // By default EventEmitters will print a warning if more than 10 listeners are added for a particular event.
emitter.listeners(event);                    // Returns an array of listeners for the specified event.
emitter.emit(event, [arg1], [arg2], [...]);  // Execute each of the listeners in order with the supplied arguments. Returns true if event had listeners, false otherwise.

EventEmitter.listenerCount(emitter, event);  // Return the number of listeners for a given event.


/* *******************************************************************************************
 * STREAM
 * http://nodejs.org/api/stream.html
 * ******************************************************************************************* */


// A stream is an abstract interface implemented by various objects in Node. For example a request to an HTTP server is a stream, as is stdout.
// Streams are readable, writable, or both. All streams are instances of EventEmitter.

// The Readable stream interface is the abstraction for a source of data that you are reading from.
// In other words, data comes out of a Readable stream.
// A Readable stream will not start emitting data until you indicate that you are ready to receive it.
// Examples of readable streams include: http responses on the client, http requests on the server, fs read streams
// zlib streams, crypto streams, tcp sockets, child process stdout and stderr, process.stdin.

var readable = getReadableStreamSomehow();

readable.on('readable', function() {});   // When a chunk of data can be read from the stream, it will emit a 'readable' event.
readable.on('data', function(chunk) {});  // If you attach a data event listener, then it will switch the stream into flowing mode, and data will be passed to your handler as soon as it is available.
readable.on('end', function() {});        // This event fires when there will be no more data to read.
readable.on('close', function() {});      // Emitted when the underlying resource (for example, the backing file descriptor) has been closed. Not all streams will emit this.
readable.on('error', function() {});      // Emitted if there was an error receiving data.

// The read() method pulls some data out of the internal buffer and returns it. If there is no data available, then it will return null.
// This method should only be called in non-flowing mode. In flowing-mode, this method is called automatically until the internal buffer is drained.
readable.read([size]);

readable.setEncoding(encoding);           // Call this function to cause the stream to return strings of the specified encoding instead of Buffer objects.
readable.resume();                        // This method will cause the readable stream to resume emitting data events.
readable.pause();                         // This method will cause a stream in flowing-mode to stop emitting data events.
readable.pipe(destination, [options]);    // This method pulls all the data out of a readable stream, and writes it to the supplied destination, automatically managing the flow so that the destination is not overwhelmed by a fast readable stream.
readable.unpipe([destination]);           // This method will remove the hooks set up for a previous pipe() call. If the destination is not specified, then all pipes are removed.
readable.unshift(chunk);                  // This is useful in certain cases where a stream is being consumed by a parser, which needs to "un-consume" some data that it has optimistically pulled out of the source, so that the stream can be passed on to some other party.


// The Writable stream interface is an abstraction for a destination that you are writing data to.
// Examples of writable streams include: http requests on the client, http responses on the server, fs write streams,
// zlib streams, crypto streams, tcp sockets, child process stdin, process.stdout, process.stderr.

var writer = getWritableStreamSomehow();

writable.write(chunk, [encoding], [callback]);  // This method writes some data to the underlying system, and calls the supplied callback once the data has been fully handled.
writer.once('drain', write);                    // If a writable.write(chunk) call returns false, then the drain event will indicate when it is appropriate to begin writing more data to the stream.

writable.end([chunk], [encoding], [callback]);  // Call this method when no more data will be written to the stream.
writer.on('finish', function() {});             // When the end() method has been called, and all data has been flushed to the underlying system, this event is emitted.
writer.on('pipe', function(src) {});            // This is emitted whenever the pipe() method is called on a readable stream, adding this writable to its set of destinations.
writer.on('unpipe', function(src) {});          // This is emitted whenever the unpipe() method is called on a readable stream, removing this writable from its set of destinations.
writer.on('error', function(src) {});           // Emitted if there was an error when writing or piping data.


// Duplex streams are streams that implement both the Readable and Writable interfaces. See above for usage.
// Examples of Duplex streams include: tcp sockets, zlib streams, crypto streams.

// Transform streams are Duplex streams where the output is in some way computed from the input. They implement both the Readable and Writable interfaces. See above for usage.
// Examples of Transform streams include: zlib streams, crypto streams.


/* *******************************************************************************************
 * FILE SYSTEM
 * http://nodejs.org/api/fs.html
 * ******************************************************************************************* */


// To use this module do require('fs').
// All the methods have asynchronous and synchronous forms.

fs.rename(oldPath, newPath, callback);  // Asynchronous rename. No arguments other than a possible exception are given to the completion callback.Asynchronous ftruncate. No arguments other than a possible exception are given to the completion callback.
fs.renameSync(oldPath, newPath);        // Synchronous rename.

fs.ftruncate(fd, len, callback);        // Asynchronous ftruncate. No arguments other than a possible exception are given to the completion callback.
fs.ftruncateSync(fd, len);              // Synchronous ftruncate.
fs.truncate(path, len, callback);       // Asynchronous truncate. No arguments other than a possible exception are given to the completion callback.
fs.truncateSync(path, len);             // Synchronous truncate.

fs.chown(path, uid, gid, callback);     // Asynchronous chown. No arguments other than a possible exception are given to the completion callback.
fs.chownSync(path, uid, gid);           // Synchronous chown.
fs.fchown(fd, uid, gid, callback);      // Asynchronous fchown. No arguments other than a possible exception are given to the completion callback.
fs.fchownSync(fd, uid, gid);            // Synchronous fchown.
fs.lchown(path, uid, gid, callback);    // Asynchronous lchown. No arguments other than a possible exception are given to the completion callback.
fs.lchownSync(path, uid, gid);          // Synchronous lchown.

fs.chmod(path, mode, callback);         // Asynchronous chmod. No arguments other than a possible exception are given to the completion callback.
fs.chmodSync(path, mode);               // Synchronous chmod.
fs.fchmod(fd, mode, callback);          // Asynchronous fchmod. No arguments other than a possible exception are given to the completion callback.
fs.fchmodSync(fd, mode);                // Synchronous fchmod.
fs.lchmod(path, mode, callback);        // Asynchronous lchmod. No arguments other than a possible exception are given to the completion callback.
fs.lchmodSync(path, mode);              // Synchronous lchmod.

fs.stat(path, callback);                // Asynchronous stat. The callback gets two arguments (err, stats) where stats is a fs.Stats object. 
fs.statSync(path);                      // Synchronous stat. Returns an instance of fs.Stats.
fs.lstat(path, callback);               // Asynchronous lstat. The callback gets two arguments (err, stats) where stats is a fs.Stats object. lstat() is identical to stat(), except that if path is a symbolic link, then the link itself is stat-ed, not the file that it refers to.
fs.lstatSync(path);                     // Synchronous lstat. Returns an instance of fs.Stats.
fs.fstat(fd, callback);                 // Asynchronous fstat. The callback gets two arguments (err, stats) where stats is a fs.Stats object. fstat() is identical to stat(), except that the file to be stat-ed is specified by the file descriptor fd.
fs.fstatSync(fd);                       // Synchronous fstat. Returns an instance of fs.Stats.

fs.link(srcpath, dstpath, callback);             // Asynchronous link. No arguments other than a possible exception are given to the completion callback.
fs.linkSync(srcpath, dstpath);                   // Synchronous link.
fs.symlink(srcpath, dstpath, [type], callback);  // Asynchronous symlink. No arguments other than a possible exception are given to the completion callback. The type argument can be set to 'dir', 'file', or 'junction' (default is 'file') and is only available on Windows (ignored on other platforms)
fs.symlinkSync(srcpath, dstpath, [type]);        // Synchronous symlink.
fs.readlink(path, callback);                     // Asynchronous readlink. The callback gets two arguments (err, linkString).
fs.readlinkSync(path);                           // Synchronous readlink. Returns the symbolic link's string value.
fs.unlink(path, callback);                       // Asynchronous unlink. No arguments other than a possible exception are given to the completion callback.
fs.unlinkSync(path);                             // Synchronous unlink.

fs.realpath(path, [cache], callback);     // Asynchronous realpath. The callback gets two arguments (err, resolvedPath).
fs.realpathSync(path, [cache]);           // Synchronous realpath. Returns the resolved path.

fs.rmdir(path, callback);                 // Asynchronous rmdir. No arguments other than a possible exception are given to the completion callback.
fs.rmdirSync(path);                       // Synchronous rmdir.
fs.mkdir(path, [mode], callback);         // Asynchronous mkdir. No arguments other than a possible exception are given to the completion callback. mode defaults to 0777.
fs.mkdirSync(path, [mode]);               // Synchronous mkdir.
fs.readdir(path, callback);               // Asynchronous readdir. Reads the contents of a directory. The callback gets two arguments (err, files) where files is an array of the names of the files in the directory excluding '.' and '..'.
fs.readdirSync(path);                     // Synchronous readdir. Returns an array of filenames excluding '.' and '..'.
fs.close(fd, callback);                   // Asynchronous close. No arguments other than a possible exception are given to the completion callback.
fs.closeSync(fd);                         // Synchronous close.
fs.open(path, flags, [mode], callback);   // Asynchronous file open.
fs.openSync(path, flags, [mode]);         // Synchronous version of fs.open().
fs.utimes(path, atime, mtime, callback);  // Change file timestamps of the file referenced by the supplied path.
fs.utimesSync(path, atime, mtime);        // Synchronous version of fs.utimes().
fs.futimes(fd, atime, mtime, callback);   // Change the file timestamps of a file referenced by the supplied file descriptor.
fs.futimesSync(fd, atime, mtime);         // Synchronous version of fs.futimes().
fs.fsync(fd, callback);                   // Asynchronous fsync. No arguments other than a possible exception are given to the completion callback.
fs.fsyncSync(fd);                         // Synchronous fsync.

fs.write(fd, buffer, offset, length, position, callback);  // Write buffer to the file specified by fd.
fs.writeSync(fd, buffer, offset, length, position);        // Synchronous version of fs.write(). Returns the number of bytes written.
fs.read(fd, buffer, offset, length, position, callback);   // Read data from the file specified by fd.
fs.readSync(fd, buffer, offset, length, position);         // Synchronous version of fs.read. Returns the number of bytesRead.
fs.readFile(filename, [options], callback);                // Asynchronously reads the entire contents of a file.
fs.readFileSync(filename, [options]);                      // Synchronous version of fs.readFile. Returns the contents of the filename. If the encoding option is specified then this function returns a string. Otherwise it returns a buffer.

fs.writeFile(filename, data, [options], callback);   // Asynchronously writes data to a file, replacing the file if it already exists. data can be a string or a buffer.
fs.writeFileSync(filename, data, [options]);         // The synchronous version of fs.writeFile.
fs.appendFile(filename, data, [options], callback);  // Asynchronously append data to a file, creating the file if it not yet exists. data can be a string or a buffer.
fs.appendFileSync(filename, data, [options]);        // The synchronous version of fs.appendFile.
fs.watch(filename, [options], [listener]);           // Watch for changes on filename, where filename is either a file or a directory. The returned object is a fs.FSWatcher. The listener callback gets two arguments (event, filename). event is either 'rename' or 'change', and filename is the name of the file which triggered the event.
fs.exists(path, callback);                           // Test whether or not the given path exists by checking with the file system. Then call the callback argument with either true or false. (should not be used)
fs.existsSync(path);                                 // Synchronous version of fs.exists. (should not be used)

// fs.Stats: objects returned from fs.stat(), fs.lstat() and fs.fstat() and their synchronous counterparts are of this type.
stats.isFile();
stats.isDirectory()
stats.isBlockDevice()
stats.isCharacterDevice()
stats.isSymbolicLink()  // (only valid with fs.lstat())
stats.isFIFO()
stats.isSocket()

fs.createReadStream(path, [options]);   // Returns a new ReadStream object.
fs.createWriteStream(path, [options]);  // Returns a new WriteStream object.


/* *******************************************************************************************
 * PATH
 * http://nodejs.org/api/fs.html
 * ******************************************************************************************* */


// Use require('path') to use this module.
// This module contains utilities for handling and transforming file paths.
// Almost all these methods perform only string transformations.
// The file system is not consulted to check whether paths are valid.

path.normalize(p);                    // Normalize a string path, taking care of '..' and '.' parts.
path.join([path1], [path2], [...]);   // Join all arguments together and normalize the resulting path.
path.resolve([from ...], to);         // Resolves 'to' to an absolute path.
path.relative(from, to);              // Solve the relative path from 'from' to 'to'.
path.dirname(p);                      // Return the directory name of a path. Similar to the Unix dirname command.
path.basename(p, [ext]);              // Return the last portion of a path. Similar to the Unix basename command.
path.extname(p);                      // Return the extension of the path, from the last '.' to end of string in the last portion of the path.

path.sep;                             // The platform-specific file separator. '\\' or '/'.
path.delimiter;                       // The platform-specific path delimiter, ';' or ':'.


/* *******************************************************************************************
 * HTTP
 * http://nodejs.org/api/http.html
 * ******************************************************************************************* */


// To use the HTTP server and client one must require('http').

http.STATUS_CODES;                                             // A collection of all the standard HTTP response status codes, and the short description of each.
http.request(options, [callback]);                             // This function allows one to transparently issue requests.
http.get(options, [callback]);                                 // Set the method to GET and calls req.end() automatically.

server = http.createServer([requestListener]);                 // Returns a new web server object. The requestListener is a function which is automatically added to the 'request' event.
server.listen(port, [hostname], [backlog], [callback]);        // Begin accepting connections on the specified port and hostname.
server.listen(path, [callback]);                               // Start a UNIX socket server listening for connections on the given path.
server.listen(handle, [callback]);                             // The handle object can be set to either a server or socket (anything with an underlying _handle member), or a {fd: <n>} object.
server.close([callback]);                                      // Stops the server from accepting new connections. 
server.setTimeout(msecs, callback);                            // Sets the timeout value for sockets, and emits a 'timeout' event on the Server object, passing the socket as an argument, if a timeout occurs.

server.maxHeadersCount;  // Limits maximum incoming headers count, equal to 1000 by default. If set to 0 - no limit will be applied.
server.timeout;          // The number of milliseconds of inactivity before a socket is presumed to have timed out.

server.on('request', function (request, response) { });        // Emitted each time there is a request.
server.on('connection', function (socket) { });                // When a new TCP stream is established.
server.on('close', function () { });                           // Emitted when the server closes.
server.on('checkContinue', function (request, response) { });  // Emitted each time a request with an http Expect: 100-continue is received.
server.on('connect', function (request, socket, head) { });    // Emitted each time a client requests a http CONNECT method.
server.on('upgrade', function (request, socket, head) { });    // Emitted each time a client requests a http upgrade.
server.on('clientError', function (exception, socket) { });    // If a client connection emits an 'error' event - it will forwarded here.

request.write(chunk, [encoding]);                              // Sends a chunk of the body.
request.end([data], [encoding]);                               // Finishes sending the request. If any parts of the body are unsent, it will flush them to the stream.
request.abort();                                               // Aborts a request.
request.setTimeout(timeout, [callback]);                       // Once a socket is assigned to this request and is connected socket.setTimeout() will be called.
request.setNoDelay([noDelay]);                                 // Once a socket is assigned to this request and is connected socket.setNoDelay() will be called.
request.setSocketKeepAlive([enable], [initialDelay]);          // Once a socket is assigned to this request and is connected socket.setKeepAlive() will be called.

request.on('response', function(response) { });                // Emitted when a response is received to this request. This event is emitted only once.
request.on('socket', function(socket) { });                    // Emitted after a socket is assigned to this request.
request.on('connect', function(response, socket, head) { });   // Emitted each time a server responds to a request with a CONNECT method. If this event isn't being listened for, clients receiving a CONNECT method will have their connections closed.
request.on('upgrade', function(response, socket, head) { });   // Emitted each time a server responds to a request with an upgrade. If this event isn't being listened for, clients receiving an upgrade header will have their connections closed.
request.on('continue', function() { });                        // Emitted when the server sends a '100 Continue' HTTP response, usually because the request contained 'Expect: 100-continue'. This is an instruction that the client should send the request body.

response.write(chunk, [encoding]);                             // This sends a chunk of the response body. If this merthod is called and response.writeHead() has not been called, it will switch to implicit header mode and flush the implicit headers.
response.writeContinue();                                      // Sends a HTTP/1.1 100 Continue message to the client, indicating that the request body should be sent.
response.writeHead(statusCode, [reasonPhrase], [headers]);     // Sends a response header to the request.
response.setTimeout(msecs, callback);                          // Sets the Socket's timeout value to msecs. If a callback is provided, then it is added as a listener on the 'timeout' event on the response object.
response.setHeader(name, value);                               // Sets a single header value for implicit headers. If this header already exists in the to-be-sent headers, its value will be replaced. Use an array of strings here if you need to send multiple headers with the same name.
response.getHeader(name);                                      // Reads out a header that's already been queued but not sent to the client. Note that the name is case insensitive.
response.removeHeader(name);                                   // Removes a header that's queued for implicit sending.
response.addTrailers(headers);                                 // This method adds HTTP trailing headers (a header but at the end of the message) to the response.
response.end([data], [encoding]);                              // This method signals to the server that all of the response headers and body have been sent; that server should consider this message complete. The method, response.end(), MUST be called on each response.

response.statusCode;                                           // When using implicit headers (not calling response.writeHead() explicitly), this property controls the status code that will be sent to the client when the headers get flushed.
response.headersSent;                                          // Boolean (read-only). True if headers were sent, false otherwise.
response.sendDate;                                             // When true, the Date header will be automatically generated and sent in the response if it is not already present in the headers. Defaults to true.

response.on('close', function () { });  // Indicates that the underlying connection was terminated before response.end() was called or able to flush.
response.on('finish', function() { });  // Emitted when the response has been sent. 

message.httpVersion;                    // In case of server request, the HTTP version sent by the client. In the case of client response, the HTTP version of the connected-to server.
message.headers;                        // The request/response headers object.
message.trailers;                       // The request/response trailers object. Only populated after the 'end' event.
message.method;                         // The request method as a string. Read only. Example: 'GET', 'DELETE'.
message.url;                            // Request URL string. This contains only the URL that is present in the actual HTTP request.
message.statusCode;                     // The 3-digit HTTP response status code. E.G. 404.
message.socket;                         // The net.Socket object associated with the connection.

message.setTimeout(msecs, callback);    // Calls message.connection.setTimeout(msecs, callback).


/* *******************************************************************************************
 * URL
 * http://nodejs.org/api/url.html
 * ******************************************************************************************* */


// This module has utilities for URL resolution and parsing. Call require('url') to use it.

url.parse(urlStr, [parseQueryString], [slashesDenoteHost]);  // Take a URL string, and return an object.
url.format(urlObj);                                          // Take a parsed URL object, and return a formatted URL string.
url.resolve(from, to);                                       // Take a base URL, and a href URL, and resolve them as a browser would for an anchor tag.


/* *******************************************************************************************
 * QUERY STRING
 * http://nodejs.org/api/querystring.html
 * ******************************************************************************************* */


// This module provides utilities for dealing with query strings. Call require('querystring') to use it.

querystring.stringify(obj, [sep], [eq]);         // Serialize an object to a query string. Optionally override the default separator ('&') and assignment ('=') characters.
querystring.parse(str, [sep], [eq], [options]);  // Deserialize a query string to an object. Optionally override the default separator ('&') and assignment ('=') characters.


/* *******************************************************************************************
 * ASSERT
 * http://nodejs.org/api/assert.html
 * ******************************************************************************************* */


// This module is used for writing unit tests for your applications, you can access it with require('assert').

assert.fail(actual, expected, message, operator);     // Throws an exception that displays the values for actual and expected separated by the provided operator.
assert(value, message); assert.ok(value, [message]);  // Tests if value is truthy, it is equivalent to assert.equal(true, !!value, message);
assert.equal(actual, expected, [message]);            // Tests shallow, coercive equality with the equal comparison operator ( == ).
assert.notEqual(actual, expected, [message]);         // Tests shallow, coercive non-equality with the not equal comparison operator ( != ).
assert.deepEqual(actual, expected, [message]);        // Tests for deep equality.
assert.notDeepEqual(actual, expected, [message]);     // Tests for any deep inequality.
assert.strictEqual(actual, expected, [message]);      // Tests strict equality, as determined by the strict equality operator ( === )
assert.notStrictEqual(actual, expected, [message]);   // Tests strict non-equality, as determined by the strict not equal operator ( !== )
assert.throws(block, [error], [message]);             // Expects block to throw an error. error can be constructor, RegExp or validation function.
assert.doesNotThrow(block, [message]);                // Expects block not to throw an error, see assert.throws for details.
assert.ifError(value);                                // Tests if value is not a false value, throws if it is a true value. Useful when testing the first argument, error in callbacks.


/* *******************************************************************************************
 * OS
 * http://nodejs.org/api/os.html
 * ******************************************************************************************* */


// Provides a few basic operating-system related utility functions.
// Use require('os') to access this module.

os.tmpdir();             // Returns the operating system's default directory for temp files.
os.endianness();         // Returns the endianness of the CPU. Possible values are "BE" or "LE".
os.hostname();           // Returns the hostname of the operating system.
os.type();               // Returns the operating system name.
os.platform();           // Returns the operating system platform.
os.arch();               // Returns the operating system CPU architecture.
os.release();            // Returns the operating system release.
os.uptime();             // Returns the system uptime in seconds.
os.loadavg();            // Returns an array containing the 1, 5, and 15 minute load averages.
os.totalmem();           // Returns the total amount of system memory in bytes.
os.freemem();            // Returns the amount of free system memory in bytes.
os.cpus();               // Returns an array of objects containing information about each CPU/core installed: model, speed (in MHz), and times (an object containing the number of milliseconds the CPU/core spent in: user, nice, sys, idle, and irq).
os.networkInterfaces();  // Get a list of network interfaces.
os.EOL;                  // A constant defining the appropriate End-of-line marker for the operating system.


/* *******************************************************************************************
 * BUFFER
 * http://nodejs.org/api/buffer.html
 * ******************************************************************************************* */


// Buffer is used to dealing with binary data
// Buffer is similar to an array of integers but corresponds to a raw memory allocation outside the V8 heap

Buffer.from(size);                                                  // Allocates a new buffer of size octets.
Buffer.from(array);                                                 // Allocates a new buffer using an array of octets.
Buffer.from(str, [encoding]);                                       // Allocates a new buffer containing the given str. encoding defaults to 'utf8'.

Buffer.isEncoding(encoding);                                        // Returns true if the encoding is a valid encoding argument, or false otherwise.
Buffer.isBuffer(obj);                                               // Tests if obj is a Buffer
Buffer.concat(list, [totalLength]);                                 // Returns a buffer which is the result of concatenating all the buffers in the list together.
Buffer.byteLength(string, [encoding]);                              // Gives the actual byte length of a string.

buf.write(string, [offset], [length], [encoding]);                  // Writes string to the buffer at offset using the given encoding
buf.toString([encoding], [start], [end]);                           // Decodes and returns a string from buffer data encoded with encoding (defaults to 'utf8') beginning at start (defaults to 0) and ending at end (defaults to buffer.length).
buf.toJSON();                                                       // Returns a JSON-representation of the Buffer instance, which is identical to the output for JSON Arrays
buf.copy(targetBuffer, [targetStart], [sourceStart], [sourceEnd]);  // Does copy between buffers. The source and target regions can be overlapped
buf.slice([start], [end]);                                          // Returns a new buffer which references the same memory as the old, but offset and cropped by the start (defaults to 0) and end (defaults to buffer.length) indexes. Negative indexes start from the end of the buffer.   
buf.fill(value, [offset], [end]);                                   // Fills the buffer with the specified value
buf[index];                                                         // Get and set the octet at index
buf.length;                                                         // The size of the buffer in bytes, Note that this is not necessarily the size of the contents

buffer.INSPECT_MAX_BYTES;                                           // How many bytes will be returned when buffer.inspect() is called. This can be overridden by user modules.

Node.js is an open-source and cross-platform JavaScript runtime environment. It is a popular tool for almost any kind of project!

Node.js runs the V8 JavaScript engine, the core of Google Chrome, outside of the browser. This allows Node.js to be very performant.

A Node.js app runs in a single process, without creating a new thread for every request. Node.js provides a set of asynchronous I/O primitives in its standard library that prevent JavaScript code from blocking and generally, libraries in Node.js are written using non-blocking paradigms, making blocking behavior the exception rather than the norm.

When Node.js performs an I/O operation, like reading from the network, accessing a database or the filesystem, instead of blocking the thread and wasting CPU cycles waiting, Node.js will resume the operations when the response comes back.

This allows Node.js to handle thousands of concurrent connections with a single server without introducing the burden of managing thread concurrency, which could be a significant source of bugs.

Node.js has a unique advantage because millions of frontend developers that write JavaScript for the browser are now able to write the server-side code in addition to the client-side code without the need to learn a completely different language.

In Node.js the new ECMAScript standards can be used without problems, as you don't have to wait for all your users to update their browsers - you are in charge of deciding which ECMAScript version to use by changing the Node.js version, and you can also enable specific experimental features by running Node.js with flags.

A Vast Number of Libraries

npm with its simple structure helped the ecosystem of Node.js proliferate, and now the npm registry hosts over 1,000,000 open source packages you can freely use.

An Example Node.js Application

The most common example Hello World of Node.js is a web server:

This code first includes the Node.js http module.

Node.js has a fantastic standard library, including first-class support for networking.

The createServer() method of http creates a new HTTP server and returns it.

The server is set to listen on the specified port and host name. When the server is ready, the callback function is called, in this case informing us that the server is running.

Whenever a new request is received, the request event is called, providing two objects: a request (an http.IncomingMessage object) and a response (an http.ServerResponse object).

Those 2 objects are essential to handle the HTTP call.

The first provides the request details. In this simple example, this is not used, but you could access the request headers and request data.

The second is used to return data to the caller.

In this case with:

JS

res.statusCode = 200

we set the statusCode property to 200, to indicate a successful response.

We set the Content-Type header:

JS

res.setHeader('Content-Type', 'text/plain')

and we close the response, adding the content as an argument to end():

JS

res.end('Hello World\n')

Node.js is a low-level platform. In order to make things easy and exciting for developers, thousands of libraries were built upon Node.js by the community.

Many of those established over time as popular options. Here is a non-comprehensive list of the ones worth learning:

• AdonisJS: A TypeScript-based fully featured framework highly focused on developer ergonomics, stability, and confidence. Adonis is one of the fastest Node.js web frameworks.
• Egg.js: A framework to build better enterprise frameworks and apps with Node.js & Koa.
• Express: It provides one of the most simple yet powerful ways to create a web server. Its minimalist approach, unopinionated, focused on the core features of a server, is key to its success.
• Fastify: A web framework highly focused on providing the best developer experience with the least overhead and a powerful plugin architecture. Fastify is one of the fastest Node.js web frameworks.
• FeatherJS: Feathers is a lightweight web-framework for creating real-time applications and REST APIs using JavaScript or TypeScript. Build prototypes in minutes and production-ready apps in days.
• Gatsby: A React-based, GraphQL powered, static site generator with a very rich ecosystem of plugins and starters.
• hapi: A rich framework for building applications and services that enables developers to focus on writing reusable application logic instead of spending time building infrastructure.
• koa: It is built by the same team behind Express, aims to be even simpler and smaller, building on top of years of knowledge. The new project born out of the need to create incompatible changes without disrupting the existing community.
• Loopback.io: Makes it easy to build modern applications that require complex integrations.
• Meteor: An incredibly powerful full-stack framework, powering you with an isomorphic approach to building apps with JavaScript, sharing code on the client and the server. Once an off-the-shelf tool that provided everything, now integrates with frontend libs React, Vue, and Angular. Can be used to create mobile apps as well.
• Micro: It provides a very lightweight server to create asynchronous HTTP microservices.
• NestJS: A TypeScript based progressive Node.js framework for building enterprise-grade efficient, reliable and scalable server-side applications.
• Next.js: React framework that gives you the best developer experience with all the features you need for production: hybrid static & server rendering, TypeScript support, smart bundling, route pre-fetching, and more.
• Nx: A toolkit for full-stack monorepo development using NestJS, Express, React, Angular, and more! Nx helps scale your development from one team building one application to many teams collaborating on multiple applications!
• Sapper: Sapper is a framework for building web applications of all sizes, with a beautiful development experience and flexible filesystem-based routing. Offers SSR and more!
• Socket.io: A real-time communication engine to build network applications.
• Strapi: Strapi is a flexible, open-source Headless CMS that gives developers the freedom to choose their favorite tools and frameworks while also allowing editors to easily manage and distribute their content. By making the admin panel and API extensible through a plugin system, Strapi enables the world's largest companies to accelerate content delivery while building beautiful digital experiences.

Node.js can be installed in different ways. This post highlights the most common and convenient ones.

Official packages for all the major platforms are available at https://nodejs.dev/download/.

One very convenient way to install Node.js is through a package manager. In this case, every operating system has its own.

Other package managers for MacOS, Linux, and Windows are listed in https://nodejs.dev/download/package-manager/

nvm is a popular way to run Node.js. It allows you to easily switch the Node.js version, and install new versions to try and easily rollback if something breaks, for example.

It is also very useful to test your code with old Node.js versions.

See https://github.com/nvm-sh/nvm for more information about this option.

In any case, when Node.js is installed you'll have access to the node executable program in the command line.

How much JavaScript do you need to know to use Node.js

As a beginner, it's hard to get to a point where you are confident enough in your programming abilities.

While learning to code, you might also be confused at where does JavaScript end, and where Node.js begins, and vice versa.

I would recommend you to have a good grasp of the main JavaScript concepts before diving into Node.js:

• Lexical Structure
• Expressions
• Types
• Classes
• Variables
• Functions
• this
• Arrow Functions
• Loops
• Scopes
• Arrays
• Template Literals
• Semicolons
• Strict Mode
• ECMAScript 6, 2016, 2017

With those concepts in mind, you are well on your road to become a proficient JavaScript developer, in both the browser and in Node.js.

The following concepts are also key to understand asynchronous programming, which is one of the fundamental parts of Node.js:

• Asynchronous programming and callbacks
• Timers
• Promises
• Async and Await
• Closures
• The Event Loop

Differences between Node.js and the Browser

Both the browser and Node.js use JavaScript as their programming language.

Building apps that run in the browser is a completely different thing than building a Node.js application.

Despite the fact that it's always JavaScript, there are some key differences that make the experience radically different.

From the perspective of a frontend developer who extensively uses JavaScript, Node.js apps bring with them a huge advantage: the comfort of programming everything - the frontend and the backend - in a single language.

You have a huge opportunity because we know how hard it is to fully, deeply learn a programming language, and by using the same language to perform all your work on the web - both on the client and on the server, you're in a unique position of advantage.

What changes is the ecosystem.

In the browser, most of the time what you are doing is interacting with the DOM, or other Web Platform APIs like Cookies. Those do not exist in Node.js, of course. You don't have the document, window and all the other objects that are provided by the browser.

And in the browser, we don't have all the nice APIs that Node.js provides through its modules, like the filesystem access functionality.

Another big difference is that in Node.js you control the environment. Unless you are building an open source application that anyone can deploy anywhere, you know which version of Node.js you will run the application on. Compared to the browser environment, where you don't get the luxury to choose what browser your visitors will use, this is very convenient.

This means that you can write all the modern ES6-7-8-9 JavaScript that your Node.js version supports.

Since JavaScript moves so fast, but browsers can be a bit slow to upgrade, sometimes on the web you are stuck with using older JavaScript / ECMAScript releases.

You can use Babel to transform your code to be ES5-compatible before shipping it to the browser, but in Node.js, you won't need that.

Another difference is that Node.js uses the CommonJS module system, while in the browser we are starting to see the ES Modules standard being implemented.

In practice, this means that for the time being you use require() in Node.js and import in the browser.

The V8 JavaScript Engine

V8 is the name of the JavaScript engine that powers Google Chrome. It's the thing that takes our JavaScript and executes it while browsing with Chrome.

V8 provides the runtime environment in which JavaScript executes. The DOM, and the other Web Platform APIs are provided by the browser.

The cool thing is that the JavaScript engine is independent of the browser in which it's hosted. This key feature enabled the rise of Node.js. V8 was chosen to be the engine that powered Node.js back in 2009, and as the popularity of Node.js exploded, V8 became the engine that now powers an incredible amount of server-side code written in JavaScript.

The Node.js ecosystem is huge and thanks to V8 which also powers desktop apps, with projects like Electron.

Other JS engines

Other browsers have their own JavaScript engine:

• Firefox has SpiderMonkey
• Safari has JavaScriptCore (also called Nitro)
• Edge was originally based on Chakra but has more recently been rebuilt using Chromium and the V8 engine.

and many others exist as well.

All those engines implement the ECMA ES-262 standard, also called ECMAScript, the standard used by JavaScript.

The quest for performance

V8 is written in C++, and it's continuously improved. It is portable and runs on Mac, Windows, Linux and several other systems.

In this V8 introduction, we will ignore the implementation details of V8: they can be found on more authoritative sites (e.g. the V8 official site), and they change over time, often radically.

V8 is always evolving, just like the other JavaScript engines around, to speed up the Web and the Node.js ecosystem.

On the web, there is a race for performance that's been going on for years, and we (as users and developers) benefit a lot from this competition because we get faster and more optimized machines year after year.

Compilation

JavaScript is generally considered an interpreted language, but modern JavaScript engines no longer just interpret JavaScript, they compile it.

This has been happening since 2009, when the SpiderMonkey JavaScript compiler was added to Firefox 3.5, and everyone followed this idea.

JavaScript is internally compiled by V8 with just-in-time (JIT) compilation to speed up the execution.

This might seem counter-intuitive, but since the introduction of Google Maps in 2004, JavaScript has evolved from a language that was generally executing a few dozens of lines of code to complete applications with thousands to hundreds of thousands of lines running in the browser.

Our applications can now run for hours inside a browser, rather than being just a few form validation rules or simple scripts.

In this new world, compiling JavaScript makes perfect sense because while it might take a little bit more to have the JavaScript ready, once done it's going to be much more performant than purely interpreted code.

Run Node.js scripts from the command line

The usual way to run a Node.js program is to run the node globally available command (once you install Node.js) and pass the name of the file you want to execute.

If your main Node.js application file is app.js, you can call it by typing:

BASH

node app.js

Above, you are explicitly telling the shell to run your script with node. You can also embed this information into your JavaScript file with a "shebang" line. The "shebang" is the first line in the file, and tells the OS which interpreter to use for running the script. Below is the first line of JavaScript:

BASH

!/usr/bin/node

Above, we are explicitly giving the absolute path of interpreter. Not all operating systems have node in the bin folder, but all should have env. You can tell the OS to run env with node as parameter:

BASH

!/usr/bin/env node

// your code

To use a shebang, your file should have executable permission. You can give app.js the executable permission by running:

BASH

chmod u+x app.js

While running the command, make sure you are in the same directory which contains the app.js file.

How to exit from a Node.js program

created: 2021-11-27T11:28:53 (UTC -05:00) tags: [] source: https://nodejs.dev/learn author:

How to exit from a Node.js program

Excerpt

Learn how to terminate a Node.js app in the best possible way

There are various ways to terminate a Node.js application.

When running a program in the console you can close it with ctrl-C, but what we want to discuss here is programmatically exiting.

Let's start with the most drastic one, and see why you're better off not using it.

The process core module provides a handy method that allows you to programmatically exit from a Node.js program: process.exit().

When Node.js runs this line, the process is immediately forced to terminate.

This means that any callback that's pending, any network request still being sent, any filesystem access, or processes writing to stdout or stderr - all is going to be ungracefully terminated right away.

If this is fine for you, you can pass an integer that signals the operating system the exit code:

JS

process.exit(1)

By default the exit code is 0, which means success. Different exit codes have different meaning, which you might want to use in your own system to have the program communicate to other programs.

You can read more on exit codes at https://nodejs.org/api/process.html#process_exit_codes

You can also set the process.exitCode property:

JS

process.exitCode = 1

and when the program ends, Node.js will return that exit code.

A program will gracefully exit when all the processing is done.

Many times with Node.js we start servers, like this HTTP server:

JS

const express = require('express')

const app = express()

app.get('/', (req, res) => {

res.send('Hi!')

})

app.listen(3000, () => console.log('Server ready'))

Express is a framework that uses the http module under the hood, app.listen() returns an instance of http. You would use https.createServer if you needed to serve your app using HTTPS, as app.listen only uses the http module.

This program is never going to end. If you call process.exit(), any currently pending or running request is going to be aborted. This is not nice.

In this case you need to send the command a SIGTERM signal, and handle that with the process signal handler:

Note: process does not require a "require", it's automatically available.

JS

const express = require('express')

const app = express()

app.get('/', (req, res) => {

res.send('Hi!')

})

const server = app.listen(3000, () => console.log('Server ready'))

process.on('SIGTERM', () => {

server.close(() => {

console.log('Process terminated')

})

})

What are signals? Signals are a POSIX intercommunication system: a notification sent to a process in order to notify it of an event that occurred.

SIGKILL is the signal that tells a process to immediately terminate, and would ideally act like process.exit().

SIGTERM is the signal that tells a process to gracefully terminate. It is the signal that's sent from process managers like upstart or supervisord and many others.

You can send this signal from inside the program, in another function:

JS

process.kill(process.pid, 'SIGTERM')

Or from another Node.js running program, or any other app running in your system that knows the PID of the process you want to terminate.