Node v0.1.90


  1. node(1)
  2. node(1)


node -- evented I/O for V8 JavaScript


An example of a web server written with Node which responds with 'Hello World':

var sys = require('sys'),
  http = require('http');

http.createServer(function (request, response) {
  response.writeHead(200, {'Content-Type': 'text/plain'});
  response.end('Hello World\n');

sys.puts('Server running at');

To run the server, put the code into a file called example.js and execute it with the node program

> node example.js
Server running at

All of the examples in the documentation can be run similarly.


Node uses the CommonJS module system.

Node has a simple module loading system. In Node, files and modules are in one-to-one correspondence. As an example, foo.js loads the module circle.js in the same directory.

The contents of foo.js:

var circle = require('./circle'),
var sys = require('sys');
sys.puts( 'The area of a circle of radius 4 is ' 
        + circle.area(4));

The contents of circle.js:

var PI = 3.14;

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

exports.circumference = function (r) {
  return 2 * PI * r;

The module circle.js has exported the functions area() and circumference(). To export an object, add to the special exports object. (Alternatively, one can use this instead of exports.) Variables local to the module will be private. In this example the variable PI is private to circle.js. The function puts() comes from the module 'sys', which is a built-in module. Modules which are not prefixed by './' are built-in module--more about this later.

A module prefixed with './' is relative to the file calling require(). That is, circle.js must be in the same directory as foo.js for require('./circle') to find it.

Without the leading './', like require('assert') the module is searched for in the require.paths array. require.paths on my system looks like this:

[ '/home/ryan/.node_libraries' ]

That is, when require('assert') is called Node looks for:

interrupting once a file is found. Files ending in '.node' are binary Addon Modules; see the section below about addons. 'index.js' allows one to package a module as a directory.

require.paths can be modified at runtime by simply unshifting new paths onto it, or at startup with the NODE_PATH environmental variable (which should be a list of paths, colon separated).

Use process.mixin() to include modules into the global namespace.

process.mixin(GLOBAL, require('./circle'), require('sys'));
puts('The area of a circle of radius 4 is ' + area(4));


Pure Javascript is Unicode friendly but not nice to pure binary data. When dealing with TCP streams or the file system, it's necessary to handle octet streams. Node has several strategies for manipulating, creating, and consuming octet streams.

Raw data is stored in instances of the Buffer class. A Buffer is similar to an array of integers but correspond to a raw memory allocation outside the V8 heap. A Buffer cannot be resized. Access the class at require('buffer').Buffer.

Node supports 3 string encodings. UTF-8 ('utf8'), ASCII ('ascii'), and Binary ('binary'). 'ascii' and 'binary' only look at the first 8 bits of the 16bit JavaScript string characters.

new Buffer(size)

Allocates a new buffer of size octets.


Get and set the octet at index. The value can be between 0x00 and 0xFF.


length in octets.

buffer.copy(targetBuffer, targetStart, start, end)

Does a memcpy() between buffers.

buffer.slice(start, end)

Returns a new buffer which references the same memory as the old, but offset and cropped by the start and end indexes. Modifying the new buffer slice will modify memory in the original buffer!

buffer.write(string, encoding, offset)

Writes string to the buffer at offset using the given encoding. Returns number of octets written. If buffer did not contain enough space to fit the entire string it will write a partial amount of the string. In the case of encoding=='utf8', the method will not write partial characters.

buffer.toString(encoding, start, end)

Decodes and returns a string assuming in the given encoding beginning at start and ending at end.


Many objects in Node emit events: a TCP server emits an event each time there is a stream, a child process emits an event when it exits. All objects which emit events are instances of events.EventEmitter.

Events are represented by a camel-cased string. Here are some examples: 'stream', 'data', 'messageBegin'.

Functions can be then be attached to objects, to be executed when an event is emitted. These functions are called listeners.

require('events').EventEmitter to access the EventEmitter class.

All EventEmitters emit the event 'newListener' when new listeners are added.

Event: 'newListener'

function (event, listener) { }

This event is made any time someone adds a new listener.

emitter.addListener(event, listener)

Adds a listener to the end of the listeners array for the specified event.

server.addListener('stream', function (stream) {
  sys.puts('someone connected!');

emitter.removeListener(event, listener)

Remove a listener from the listener array for the specified event. Caution: changes array indices in the listener array behind the listener.


Removes all listeners from the listener array for the specified event.


Returns an array of listeners for the specified event. This array can be manipulated, e.g. to remove listeners.

emitter.emit(event, arg1, arg2, ...)

Execute each of the listeners in order with the supplied arguments.


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.

Readable Stream

A readable stream has the following methods, members, and events.

Event: 'data'

function (data) { }

The 'data' event emits either a Buffer (by default) or a string if setEncoding() was used.

Event: 'end'

function () { }

Emitted when the stream has received an EOF (FIN in TCP terminology). Indicates that no more 'data' events will happen. If the stream is also writable, it may be possible to continue writing.

Event: 'error'

function (exception) { }

Emitted if there was an error receiving data.

Event: 'close'

function () { }

Emitted when the underlying file descriptor has be closed. Not all streams will emit this. (For example, an incoming HTTP request will not emit 'close'.)


Makes the data event emit a string instead of a Buffer. encoding can be 'utf8', 'ascii', or 'binary'.


Pauses the incoming 'data' events.


Resumes the incoming 'data' events after a pause().


Closes the underlying file descriptor. Stream will not emit any more events.

Writable Stream

A writable stream has the following methods, members, and events.

Event: 'drain'

function () { }

Emitted after a write() method was called that returned false to indicate that it is safe to write again.

Event: 'error'

function (exception) { }

Emitted on error with the exception e.

Event: 'close'

function () { }

Emitted when the underlying file descriptor has been closed.

stream.write(string, encoding)

Writes string with the given encoding to the stream. Returns true if the string has been flushed to the kernel buffer. Returns false to indicate that the kernel buffer is full, and the data will be sent out in the future. The 'drain' event will indicate when the kernel buffer is empty again. The encoding defaults to 'utf8'.


Same as the above except with a raw buffer.


Terminates the stream with EOF or FIN.

stream.end(string, encoding)

Sends string with the given encoding and terminates the stream with EOF or FIN. This is useful to reduce the number of packets sent.


Same as above but with a buffer.


Closes the underlying file descriptor. Stream will not emit any more events.

Global Objects

These object are available in the global scope and can be accessed from anywhere.


The global namespace object.


The process object. Most stuff lives in here. See the 'process object' section.


To require modules. See the modules section.


The search path for absolute path arguments to require().


The filename of the script being executed.


The dirname of the script being executed.


A reference to the current module (of type process.Module). In particular module.exports is the same as the exports object. See src/process.js for more information.


The process object is a global object and can be accessed from anywhere. It is an instance of EventEmitter.

Event: 'exit'

function () {}

Emitted when the process is about to exit. This is a good hook to perform constant time checks of the module's state (like for unit tests). The main event loop will no longer be run after the 'exit' callback finishes, so timers may not be scheduled.

Example of listening for exit:

var sys = require('sys');

process.addListener('exit', function () {
  process.nextTick(function () {
   sys.puts('This will not run');
  sys.puts('About to exit.');

Event: 'uncaughtException'

function (err) { }

Emitted when an exception bubbles all the way back to the event loop. If a listener is added for this exception, the default action (which is to print a stack trace and exit) will not occur.

Example of listening for uncaughtException:

var sys = require('sys');

process.addListener('uncaughtException', function (err) {
  sys.puts('Caught exception: ' + err);

setTimeout(function () {
  sys.puts('This will still run.');
}, 500);

// Intentionally cause an exception, but don't catch it.
sys.puts('This will not run.');

Note that uncaughtException is a very crude mechanism for exception handling. Using try / catch in your program will give you more control over your program's flow. Especially for server programs that are designed to stay running forever, uncaughtException can be a useful safety mechanism.

Signal Events

function () {}

Emitted when the processes receives a signal. See sigaction(2) for a list of standard POSIX signal names such as SIGINT, SIGUSR1, etc.

Example of listening for SIGINT:

var sys = require('sys'),
    stdin = process.openStdin();

process.addListener('SIGINT', function () {
  sys.puts('Got SIGINT.  Press Control-D to exit.');

An easy way to send the SIGINT signal is with Control-C in most terminal programs.


A writable stream to stdout.

Example: the definition of sys.puts

exports.puts = function (d) {
  process.stdout.write(d + '\n');


Opens the standard input stream, returns a readable stream.

Example of opening standard input and listening for both events:

var stdin = process.openStdin();


stdin.addListener('data', function (chunk) {
  process.stdout.write('data: ' + chunk);

stdin.addListener('end', function () {


An array containing the command line arguments. The first element will be 'node', the second element will be the name of the JavaScript file. The next elements will be any additional command line arguments.

// print process.argv
var sys = require('sys');

process.argv.forEach(function (val, index, array) {
  sys.puts(index + ': ' + val);

This will generate:

$ node process-2.js one two=three four
0: node
1: /Users/mjr/work/node_docs/data/v0.1.31/examples/process-2.js
2: one
3: two=three
4: four


Changes the current working directory of the process or throws an exception if that fails.

var sys = require('sys');

sys.puts('Starting directory: ' + process.cwd());
try {
  sys.puts('New directory: ' + process.cwd());
catch (err) {
  sys.puts('chdir: ' + err);

process.compile(code, filename)

Similar to eval except that you can specify a filename for better error reporting and the code cannot see the local scope. The value of filename will be used as a filename if a stack trace is generated by the compiled code.

Example of using process.compile and eval to run the same code:

var sys = require('sys'),
    localVar = 123,
    compiled, evaled;

compiled = process.compile('localVar = 1;', 'myfile.js');
sys.puts('localVar: ' + localVar + ', compiled: ' + compiled);
evaled = eval('localVar = 1;');
sys.puts('localVar: ' + localVar + ', evaled: ' + evaled);

// localVar: 123, compiled: 1
// localVar: 1, evaled: 1

process.compile does not have access to the local scope, so localVar is unchanged. eval does have access to the local scope, so localVar is changed.

See also: process.evalcx


Returns the current working directory of the process.

require('sys').puts('Current directory: ' + process.cwd());


An object containing the user environment. See environ(7).

process.evalcx(code, sandbox, filename)

Similar to eval and process.compile. process.evalcx compiles code to run in sandbox as if it were loaded from filename. The object sandbox will be used as the global object for code. sandbox and filename are optional.

var sys = require('sys'),
    sandbox = {
      animal: 'cat',
      count: 2

process.evalcx('count += 1; name = 'kitty'', sandbox, 'myfile.js');

Note that running untrusted code is a tricky business requiring great care. To prevent accidental global variable leakage, process.evalcx is quite useful, but to safely run untrusted code, many more steps must be taken.


Ends the process with the specified code. If omitted, exit uses the 'success' code 0.

To exit with a 'failure' code:


The shell that executed node should see the exit code as 1.

process.getgid(), process.setgid(id)

Gets/sets the group identity of the process. (See setgid(2).) This is the numerical group id, not the group name.

var sys = require('sys');

sys.puts('Current gid: ' + process.getgid());
try {
  sys.puts('New gid: ' + process.getgid());
catch (err) {
  sys.puts('Failed to set gid: ' + err);

process.getuid(), process.setuid(id)

Gets/sets the user identity of the process. (See setuid(2).) This is the numerical userid, not the username.

var sys = require('sys');

sys.puts('Current uid: ' + process.getuid());
try {
  sys.puts('New uid: ' + process.getuid());
catch (err) {
  sys.puts('Failed to set uid: ' + err);


A compiled-in property that exposes NODE_PREFIX.

require('sys').puts('Install prefix: ' + process.installPrefix);

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. Signal names are strings like 'SIGINT' or 'SIGUSR1'. If omitted, the signal will be 'SIGINT'. See kill(2) for more information.

Note that just because the name of this function is process.kill, it is really just a signal sender, like the kill system call. The signal sent may do something other than kill the target process.

Example of sending a signal to yourself:

var sys = require('sys');

process.addListener('SIGHUP', function () {
  sys.puts('Got SIGHUP signal.');

setTimeout(function () {
}, 100);

process.kill(, 'SIGHUP');

The PID of the process.

require('sys').puts('This process is pid ' +;


What platform you're running on. 'linux2', 'darwin', etc.

require('sys').puts('This platform is ' + process.platform);


Returns an object describing the memory usage of the Node process.

var sys = require('sys');


This will generate:

{ rss: 4935680
, vsize: 41893888
, heapTotal: 1826816
, heapUsed: 650472

heapTotal and heapUsed refer to V8's memory usage.


On the next loop around the event loop call this callback. This is not a simple alias to setTimeout(fn, 0), it's much more efficient.

var sys = require('sys');

process.nextTick(function () {
  sys.puts('nextTick callback');


Sets or read the process's file mode creation mask. Child processes inherit the mask from the parent process. Returns the old mask if mask argument is given, otherwise returns the current mask.

var sys = require('sys'),
    oldmask, newmask = 0644;

oldmask = process.umask(newmask);
// these octal numbers don't display right in JavaScript
sys.puts('Changed umask from: ' + oldmask + ' to ' + newmask);


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


Outputs string and a trailing new-line to stdout.

require('sys').puts('String with a newline');


Like puts() but without the trailing new-line.

require('sys').print('String with no newline');


A synchronous output function. Will block the process and output string immediately to stderr.

require('sys').debug('message on stderr');


Output with timestamp on stdout.

require('sys').log('Timestmaped message.');

sys.inspect(object, showHidden, depth)

Return a string representation of object, which is useful for debugging.

If showHidden is true, then the object's non-enumerable properties will be shown too.

If depth is provided, it tells inspect how many times to recurse while formatting the object. This is useful for inspecting large complicated objects.

The default is to only recurse twice. To make it recurse indefinitely, pass in null for depth.

Example of inspecting all properties of the sys object:

var sys = require('sys');

sys.puts(sys.inspect(sys, true, null));


setTimeout(callback, delay, [arg, ...])

To schedule execution of callback after delay milliseconds. Returns a timeoutId for possible use with clearTimeout().


Prevents a timeout from triggering.

setInterval(callback, delay, [arg, ...])

To schedule the repeated execution of callback every delay milliseconds. Returns a intervalId for possible use with clearInterval().

Optionally, you can also pass arguments to the callback.


Stops a interval from triggering.

Child Processes

Node provides a tri-directional popen(3) facility through the ChildProcess class.

It is possible to stream data through the child's stdin, stdout, and stderr in a fully non-blocking way.

To create a child process use require('child_process').spawn().

Child processes always have three streams associated with them. child.stdin, child.stdout, and child.stderr.

ChildProcess is an EventEmitter.

Event: 'exit'

function (code) {}

This event is emitted after the child process ends. code is the final exit code of the process. After this event is emitted, the 'output' and 'error' callbacks will no longer be made.

child_process.spawn(command, args, env)

Launches a new process with the given command, command line arguments, and environment variables. If omitted, args defaults to an empty Array, and env defaults to process.env.

Example of running ls -lh /usr, capturing stdout, stderr, and the exit code:

var sys   = require('sys'),
    spawn = require('child_process').spawn,
    ls    = spawn('ls', ['-lh', '/usr']);

ls.stdout.addListener('data', function (data) {
  sys.print('stdout: ' + data);

ls.stderr.addListener('data', function (data) {
  sys.print('stderr: ' + data);

ls.addListener('exit', function (code) {
  sys.puts('child process exited with code ' + code);

Example of checking for failed exec:

var sys   = require('sys'),
    spawn = require('child_process').spawn,
    child = spawn('bad_command');

child.stderr.addListener('data', function (data) {
  if (/^execvp\(\)/.test(data.asciiSlice(0,data.length))) {
    sys.puts('Failed to start child process.');

See also: child_process.exec()


Send a signal to the child process. If no argument is given, the process will be sent 'SIGTERM'. See signal(7) for a list of available signals.

var sys   = require('sys'),
    spawn = require('child_process').spawn,
    grep  = spawn('grep', ['ssh']);

grep.addListener('exit', function (code) {
  sys.puts('child process exited with code ' + code);

// send SIGHUP to process

Note that while the function is called kill, the signal delivered to the child process may not actually kill it. kill really just sends a signal to a process.

See kill(2)

The PID of the child process.


var sys   = require('sys'),
    spawn = require('child_process').spawn,
    grep  = spawn('grep', ['ssh']);

sys.puts('Spawned child pid: ' +;

child.stdin.write(data, encoding)

Write data to the child process's stdin. The second argument is optional and specifies the encoding: possible values are 'utf8', 'ascii', and 'binary'.

Example: A very elaborate way to run 'ps ax | grep ssh'

var sys   = require('sys'),
    spawn = require('child_process').spawn,
    ps    = spawn('ps', ['ax']),
    grep  = spawn('grep', ['ssh']);

ps.stdout.addListener('data', function (data) {

ps.stderr.addListener('data', function (data) {
  sys.print('ps stderr: ' + data);

ps.addListener('exit', function (code) {
  if (code !== 0) {
    sys.puts('ps process exited with code ' + code);

grep.stdout.addListener('data', function (data) {

grep.stderr.addListener('data', function (data) {
  sys.print('grep stderr: ' + data);

grep.addListener('exit', function (code) {
  if (code !== 0) {
    sys.puts('grep process exited with code ' + code);


Closes the child process's stdin stream. This often causes the child process to terminate.


var sys   = require('sys'),
    spawn = require('child_process').spawn,
    grep  = spawn('grep', ['ssh']);

grep.addListener('exit', function (code) {
  sys.puts('child process exited with code ' + code);


child_process.exec(command, callback)

High-level way to execute a command as a child process, buffer the output, and return it all in a callback.

var sys   = require('sys'),
    exec  = require('child_process').exec,

child = exec('cat *.js bad_file | wc -l', function (error, stdout, stderr) {
  sys.print('stdout: ' + stdout);
  sys.print('stderr: ' + stderr);
  if (error !== null) {
    sys.puts('exec error: ' + error);

The callback gets the arguments (error, stdout, stderr). On success, error will be null. On error, error will be an instance of Error and err.code will be the exit code of the child process.

File System

File I/O is provided by simple wrappers around standard POSIX functions. To use this module do require('fs'). All the methods have asynchronous and synchronous forms.

The asynchronous form always take a completion callback as its last argument. The arguments passed to the completion callback depend on the method, but the first argument is always reserved for an exception. If the operation was completed successfully, then the first argument will be null or undefined.

Here is an example of the asynchronous version:

var fs = require('fs'),
    sys = require('sys');

fs.unlink('/tmp/hello', function (err) {
  if (err) throw err;
  sys.puts('successfully deleted /tmp/hello');

Here is the synchronous version:

var fs = require('fs'),
    sys = require('sys');

sys.puts('successfully deleted /tmp/hello');

With the asynchronous methods there is no guaranteed ordering. So the following is prone to error:

fs.rename('/tmp/hello', '/tmp/world', function (err) {
  if (err) throw err;
  sys.puts('renamed complete');
fs.stat('/tmp/world', function (err, stats) {
  if (err) throw err;
  sys.puts('stats: ' + JSON.stringify(stats));

It could be that fs.stat is executed before fs.rename. The correct way to do this is to chain the callbacks.

fs.rename('/tmp/hello', '/tmp/world', function (err) {
  if (err) throw err;
  fs.stat('/tmp/world', function (err, stats) {
    if (err) throw err;
    sys.puts('stats: ' + JSON.stringify(stats));

In busy processes, the programmer is strongly encouraged to use the asynchronous versions of these calls. The synchronous versions will block the entire process until they complete--halting all connections.

fs.rename(path1, path2, callback)

Asynchronous rename(2). No arguments other than a possible exception are given to the completion callback.

fs.renameSync(path1, path2)

Synchronous rename(2).

fs.truncate(fd, len, callback)

Asynchronous ftruncate(2). No arguments other than a possible exception are given to the completion callback.

fs.truncateSync(fd, len)

Synchronous ftruncate(2).

fs.chmod(path, mode, callback)

Asynchronous chmod(2). No arguments other than a possible exception are given to the completion callback.

fs.chmodSync(path, mode)

Synchronous chmod(2).

fs.stat(path, callback), fs.lstat(path, callback)

Asynchronous stat(2) or lstat(2). The callback gets two arguments (err, stats) where stats is a fs.Stats object. It looks like this:

{ dev: 2049
, ino: 305352
, mode: 16877
, nlink: 12
, uid: 1000
, gid: 1000
, rdev: 0
, size: 4096
, blksize: 4096
, blocks: 8
, atime: '2009-06-29T11:11:55Z'
, mtime: '2009-06-29T11:11:40Z'
, ctime: '2009-06-29T11:11:40Z' 

See the fs.Stats section below for more information.

fs.statSync(path), fs.lstatSync(path)

Synchronous stat(2) or lstat(2). Returns an instance of fs.Stats., dstpath, callback)

Asynchronous link(2). No arguments other than a possible exception are given to the completion callback.

fs.linkSync(dstpath, srcpath)

Synchronous link(2).

fs.symlink(linkdata, path, callback)

Asynchronous symlink(2). No arguments other than a possible exception are given to the completion callback.

fs.symlinkSync(linkdata, path)

Synchronous symlink(2).

fs.readlink(path, callback)

Asynchronous readlink(2). The callback gets two arguments (err, resolvedPath).


Synchronous readlink(2). Returns the resolved path.

fs.realpath(path, callback)

Asynchronous realpath(2). The callback gets two arguments (err, resolvedPath).


Synchronous realpath(2). Returns the resolved path.

fs.unlink(path, callback)

Asynchronous unlink(2). No arguments other than a possible exception are given to the completion callback.


Synchronous unlink(2).

fs.rmdir(path, callback)

Asynchronous rmdir(2). No arguments other than a possible exception are given to the completion callback.


Synchronous rmdir(2).

fs.mkdir(path, mode, callback)

Asynchronous mkdir(2). No arguments other than a possible exception are given to the completion callback.

fs.mkdirSync(path, mode)

Synchronous mkdir(2).

fs.readdir(path, callback)

Asynchronous readdir(3). 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 '..'.


Synchronous readdir(3). Returns an array of filenames excluding '.' and '..'.

fs.close(fd, callback)

Asynchronous close(2). No arguments other than a possible exception are given to the completion callback.


Synchronous close(2)., flags, mode, callback)

Asynchronous file open. See open(2). Flags can be 'r', 'r+', 'w', 'w+', 'a', or 'a+'. The callback gets two arguments (err, fd).

fs.openSync(path, flags, mode)

Synchronous open(2).

fs.write(fd, data, position, encoding, callback)

Write data to the file specified by fd. position refers to the offset from the beginning of the file where this data should be written. If position is null, the data will be written at the current position. See pwrite(2).

The callback will be given two arguments (err, written) where written specifies how many bytes were written.

fs.writeSync(fd, data, position, encoding)

Synchronous version of fs.write(). Returns the number of bytes written., length, position, encoding, callback)

Read data from the file specified by fd.

length is an integer specifying the number of bytes to read.

position is an integer specifying where to begin reading from in the file.

The callback is given three arguments, (err, data, bytesRead) where data is a string--what was read--and bytesRead is the number of bytes read.

fs.readSync(fd, length, position, encoding)

Synchronous version of Returns an array [data, bytesRead].

fs.readFile(filename, encoding='utf8', callback)

Asynchronously reads the entire contents of a file. Example:

fs.readFile('/etc/passwd', function (err, data) {
  if (err) throw err;

The callback is passed two arguments (err, data), where data is the contents of the file.

fs.readFileSync(filename, encoding='utf8')

Synchronous version of fs.readFile. Returns the contents of the filename.

fs.writeFile(filename, data, encoding='utf8', callback)

Asynchronously writes data to a file. Example:

fs.writeFile('message.txt', 'Hello Node', function (err) {
  if (err) throw err;
  sys.puts('It's saved!');

fs.writeFileSync(filename, data, encoding='utf8')

The synchronous version of fs.writeFile.

fs.watchFile(filename, [options,] listener)

Watch for changes on filename. The callback listener will be called each time the file changes.

The second argument is optional. The options if provided should be an object containing two members a boolean, persistent, and interval, a polling value in milliseconds. The default is {persistent: true, interval: 0}.

The listener gets two arguments the current stat object and the previous stat object:

fs.watchFile(f, function (curr, prev) {
  sys.puts('the current mtime is: ' + curr.mtime);
  sys.puts('the previous mtime was: ' + prev.mtime);

These stat objects are instances of fs.Stat.


Stop watching for changes on filename.


Objects returned from fs.stat() and fs.lstat() are of this type.


FileReadStream is a readable stream.

fs.createReadStream(path, [options])

Returns a new FileReadStream object.

options is an object with the following defaults:

{ 'flags': 'r'
, 'encoding': 'binary'
, 'mode': 0666
, 'bufferSize': 4 * 1024


A boolean that is true by default, but turns false after an 'error' occured, the stream came to an 'end', or destroy() was called.


Stops the stream from reading further data. No 'data' event will be fired until the stream is resumed.


Resumes the stream. Together with pause() this useful to throttle reading.


Allows to close the stream before the 'end' is reached. No more events other than 'close' will be fired after this method has been called.


FileWriteStream is a writable stream.

fs.createWriteStream(path, [options])

Returns a new FileWriteStream object. options is an object with the following defaults:

{ 'flags': 'w'
, 'encoding': 'binary'
, 'mode': 0666


A boolean that is true by default, but turns false after an 'error' occurred or end() / destroy() was called.


Returns true if the data was flushed to the kernel, and false if it was queued up for being written later. A 'drain' will fire after all queued data has been written.

You can also specify callback to be notified when the data from this write has been flushed. The first param is err, the second is bytesWritten.


Closes the stream right after all queued write() calls have finished.


Allows to close the stream regardless of its current state.


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

The HTTP interfaces in Node are designed to support many features of the protocol which have been traditionally difficult to use. In particular, large, possibly chunk-encoded, messages. The interface is careful to never buffer entire requests or responses--the user is able to stream data.

HTTP message headers are represented by an object like this:

{ 'content-length': '123'
, 'content-type': 'text/plain'
, 'stream': 'keep-alive'
, 'accept': '*/*'

Keys are lowercased. Values are not modified.

In order to support the full spectrum of possible HTTP applications, Node's HTTP API is very low-level. It deals with stream handling and message parsing only. It parses a message into headers and body but it does not parse the actual headers or the body.


This is an EventEmitter with the following events:

Event: 'request'

function (request, response) { }

request is an instance of http.ServerRequest and response is an instance of http.ServerResponse

Event: 'stream'

function (stream) { }

When a new TCP stream is established. stream is an object of type http.Connection. Usually users will not want to access this event. The stream can also be accessed at

Event: 'close'

function (errno) { }

Emitted when the server closes.

http.createServer(request_listener, [options])

Returns a new web server object.

The options argument is optional. The options argument accepts the same values as the options argument for net.Server.

The request_listener is a function which is automatically added to the 'request' event.

server.listen(port, hostname)

Begin accepting connections on the specified port and hostname. If the hostname is omitted, the server will accept connections directed to any address.

To listen to a unix socket, supply a filename instead of port and hostname.

This function is asynchronous. listening will be emitted when the server is ready to accept connections.


Start an HTTP UNIX socket server listening for connections on the given path. (Hint: use NGINX to load balance across many Node servers with this.)

This function is asynchronous. listening will be emitted when the server is ready to accept connections.


Stops the server from accepting new connections.


This object is created internally by a HTTP server--not by the user--and passed as the first argument to a 'request' listener.

This is an EventEmitter with the following events:

'data' - callback(chunk)
Emitted when a piece of the message body is received.

Example: A chunk of the body is given as the single argument. The transfer-encoding has been decoded. The body chunk is a string. The body encoding is set with request.setBodyEncoding().

'end' - callback()
Emitted exactly once for each message. No arguments. After emitted no other events will be emitted on the request.


The request method as a string. Read only. Example: 'GET', 'DELETE'.


Request URL string. This contains only the URL that is present in the actual HTTP request. If the request is:

GET /status?name=ryan HTTP/1.1\r\n
Accept: text/plain\r\n

Then request.url will be:


If you would like to parse the URL into its parts, you can use require('url').parse(request.url). Example:

node> require('url').parse('/status?name=ryan')
{ href: '/status?name=ryan'
, search: '?name=ryan'
, query: 'name=ryan'
, pathname: '/status'

If you would like to extract the params from the query string, you can use the require('querystring').parse function, or pass true as the second argument to require('url').parse. Example:

node> require('url').parse('/status?name=ryan', true)
{ href: '/status?name=ryan'
, search: '?name=ryan'
, query: { name: 'ryan' }
, pathname: '/status'


Read only.


The HTTP protocol version as a string. Read only. Examples: '1.1', '1.0'


Set the encoding for the request body. Either 'utf8' or 'binary'. Defaults to 'binary'.


Pauses request from emitting events. Useful to throttle back an upload.


Resumes a paused request.


The net.Stream object assocated with the connection.


This object is created internally by a HTTP server--not by the user. It is passed as the second parameter to the 'request' event. It is a writable stream.

response.writeHead(statusCode[, reasonPhrase] , headers)

Sends a response header to the request. The status code is a 3-digit HTTP status code, like 404. The last argument, headers, are the response headers. Optionally one can give a human-readable reasonPhrase as the second argument.


var body = 'hello world';
response.writeHead(200, {
  'Content-Length': body.length,
  'Content-Type': 'text/plain'

This method must only be called once on a message and it must be called before response.end() is called.

response.write(chunk, encoding)

This method must be called after writeHead was called. It sends a chunk of the response body. This method may be called multiple times to provide successive parts of the body.

If chunk is a string, the second parameter specifies how to encode it into a byte stream. By default the encoding is 'ascii'.

Note: This is the raw HTTP body and has nothing to do with higher-level multi-part body encodings that may be used.

The first time response.write() is called, it will send the buffered header information and the first body to the client. The second time response.write() is called, Node assumes you're going to be streaming data, and sends that separately. That is, the response is buffered up to the first chunk of body.


This method signals to the server that all of the response headers and body has been sent; that server should consider this message complete. The method, response.end(), MUST be called on each response.


An HTTP client is constructed with a server address as its argument, the returned handle is then used to issue one or more requests. Depending on the server connected to, the client might pipeline the requests or reestablish the stream after each stream. Currently the implementation does not pipeline requests.

Example of connecting to

var sys = require('sys'),
   http = require('http');
var google = http.createClient(80, '');
var request = google.request('GET', '/', {'host': ''});
request.addListener('response', function (response) {
  sys.puts('STATUS: ' + response.statusCode);
  sys.puts('HEADERS: ' + JSON.stringify(response.headers));
  response.addListener('data', function (chunk) {
    sys.puts('BODY: ' + chunk);

http.createClient(port, host)

Constructs a new HTTP client. port and host refer to the server to be connected to. A stream is not established until a request is issued.

client.request([method], path, [request_headers])

Issues a request; if necessary establishes stream. Returns a http.ClientRequest instance.

method is optional and defaults to 'GET' if omitted.

request_headers is optional. Additional request headers might be added internally by Node. Returns a ClientRequest object.

Do remember to include the Content-Length header if you plan on sending a body. If you plan on streaming the body, perhaps set Transfer-Encoding: chunked.

NOTE: the request is not complete. This method only sends the header of the request. One needs to call request.end() to finalize the request and retrieve the response. (This sounds convoluted but it provides a chance for the user to stream a body to the server with request.write().)


This object is created internally and returned from the request() method of a http.Client. It represents an in-progress request whose header has already been sent.

To get the response, add a listener for 'response' to the request object. 'response' will be emitted from the request object when the response headers have been received. The 'response' event is executed with one argument which is an instance of http.ClientResponse.

During the 'response' event, one can add listeners to the response object; particularly to listen for the 'data' event. Note that the 'response' event is called before any part of the response body is received, so there is no need to worry about racing to catch the first part of the body. As long as a listener for 'data' is added during the 'response' event, the entire body will be caught.

// Good
request.addListener('response', function (response) {
  response.addListener('data', function (chunk) {
    sys.puts('BODY: ' + chunk);

// Bad - misses all or part of the body
request.addListener('response', function (response) {
  setTimeout(function () {
    response.addListener('data', function (chunk) {
      sys.puts('BODY: ' + chunk);
  }, 10);

This is a writable stream. This is an EventEmitter with the following events:

'response' - callback(response)
Emitted when a response is received to this request. This event is emitted only once. The response argument will be an instance of http.ClientResponse.

request.write(chunk, encoding='ascii')

Sends a chunk of the body. By calling this method many times, the user can stream a request body to a server--in that case it is suggested to use the ['Transfer-Encoding', 'chunked'] header line when creating the request.

The chunk argument should be an array of integers or a string.

The encoding argument is optional and only applies when chunk is a string. The encoding argument should be either 'utf8' or 'ascii'. By default the body uses ASCII encoding, as it is faster.


Finishes sending the request. If any parts of the body are unsent, it will flush them to the stream. If the request is chunked, this will send the terminating '0\r\n\r\n'.


This object is created when making a request with http.Client. It is passed to the 'response' event of the request object.

The response implements the readable stream interface.

Event: 'data'

function (chunk) {}

Emitted when a piece of the message body is received.

Example: A chunk of the body is given as the single
argument. The transfer-encoding has been decoded.  The
body chunk a String.  The body encoding is set with

Event: 'end'

function () {}

Emitted exactly once for each message. No arguments. After emitted no other events will be emitted on the response.


The 3-digit HTTP response status code. E.G. 404.


The HTTP version of the connected-to server. Probably either '1.1' or '1.0'.


The response headers.


Set the encoding for the response body. Either 'utf8' or 'binary'. Defaults to 'binary'.


Pauses response from emitting events. Useful to throttle back a download.


Resumes a paused response.


A reference to the http.Client that this response belongs to.


This class is used to create a TCP or UNIX server.

Here is an example of a echo server which listens for connections on port 7000:

var net = require('net');
var server = net.createServer(function (stream) {
  stream.addListener('connect', function () {
  stream.addListener('data', function (data) {
  stream.addListener('end', function () {
server.listen(7000, 'localhost');

To listen on the socket '/tmp/echo.sock', the last line would just be changed to


This is an EventEmitter with the following events:

Event: 'listening'

function () {}

After listen() is called, this event will notify that the server is ready to accept connections.

Event: 'connection'

function (stream) {}

Emitted when a new connection is made. stream is an instance of net.Stream.

Event: 'close'

function () {}

Emitted when the server closes.


Creates a new TCP server. The connection_listener argument is automatically set as a listener for the 'connection' event.

server.listen(port, host=null)

Tells the server to listen for TCP connections to port and host.

host is optional. If host is not specified the server will accept client connections on any network address.

This function is asynchronous. The server will emit 'listening' when it is safe to connect to it.


Stops the server from accepting new connections. This function is asynchronous, the server is finally closed when the server emits a 'close' event.


This object is an abstraction of of a TCP or UNIX socket. net.Stream instance implement a duplex stream interface. They can be created by the user and used as a client (with connect()) or they can be created by Node and passed to the user through the 'connection' event of a server.

net.Stream instances are an EventEmitters with the following events:

Event: 'connect'

function () { }

Emitted when a stream connection successfully is established. See connect().

Event: 'data'

function (data) { }

Emitted when data is received. The argument data will be a Buffer or String. Encoding of data is set by stream.setEncoding(). (See the section on Readable Streams for more infromation.)

Event: 'end'

function () { }

Emitted when the other end of the stream sends a FIN packet. After this is emitted the readyState will be 'writeOnly'. One should probably just call stream.end() when this event is emitted.

Event: 'timeout'

function () { }

Emitted if the stream times out from inactivity. The 'close' event will be emitted immediately following this event.

Event: 'drain'

function () { }

Emitted when the write buffer becomes empty. Can be used to throttle uploads.

Event: 'error'

function (exception) { }

Emitted when an error occurs. The 'close' event will be called directly following this event.

Event: 'close'

function () { }

Emitted once the stream is fully closed. The argument had_error is a boolean which says if the stream was closed due to a transmission error.

net.createConnection(port, host='')

Construct a new stream object and opens a stream to the specified port and host. If the second parameter is omitted, localhost is assumed.

When the stream is established the 'connect' event will be emitted.

stream.connect(port, host='')

Opens a stream to the specified port and host. createConnection() also opens a stream; normally this method is not needed. Use this only if a stream is closed and you want to reuse the object to connect to another server.

This function is asynchronous. When the 'connect' event is emitted the stream is established. If there is a problem connecting, the 'connect' event will not be emitted, the 'error' event will be emitted with the exception.


The string representation of the remote IP address. For example, '' or '2001:4860:a005::68'.

This member is only present in server-side connections.


Either 'closed', 'open', 'opening', 'readOnly', or 'writeOnly'.


Sets the encoding (either 'ascii', 'utf8', or 'binary') for data that is received.

stream.write(data, encoding='ascii')

Sends data on the stream. The second parameter specifies the encoding in the case of a string--it defaults to ASCII because encoding to UTF8 is rather slow.

Returns true if the entire data was flushed successfully to the kernel buffer. Returns false if all or part of the data was queued in user memory. 'drain' will be emitted when the buffer is again free.


Half-closes the stream. I.E., it sends a FIN packet. It is possible the server will still send some data. After calling this readyState will be 'readOnly'.


Ensures that no more I/O activity happens on this stream. Only necessary in case of errors (parse error or so).


Pauses the reading of data. That is, 'data' events will not be emitted. Useful to throttle back an upload.


Resumes reading after a call to pause().


Sets the stream to timeout after timeout milliseconds of inactivity on the stream. By default all net.Stream objects have a timeout of 60 seconds (60000 ms).

If timeout is 0, then the idle timeout is disabled.


Disables the Nagle algorithm. By default TCP connections use the Nagle algorithm, they buffer data before sending it off. Setting noDelay will immediately fire off data each time stream.write() is called.


Use require('dns') to access this module.

Here is an example which resolves '' then reverse resolves the IP addresses which are returned.

var dns = require('dns'),
    sys = require('sys');

dns.resolve4('', function (err, addresses) {
  if (err) throw err;

  sys.puts('addresses: ' + JSON.stringify(addresses));

  for (var i = 0; i < addresses.length; i++) {
    var a = addresses[i];
    dns.reverse(a, function (err, domains) {
      if (err) {
        puts('reverse for ' + a + ' failed: ' + e.message);
      } else {
        sys.puts('reverse for ' + a + ': ' + JSON.stringify(domains));

dns.resolve(domain, rrtype = 'A', callback)

Resolves a domain (e.g. '') into an array of the record types specified by rrtype. Valid rrtypes are A (IPV4 addresses), AAAA (IPV6 addresses), MX (mail exchange records), TXT (text records), SRV (SRV records), and PTR (used for reverse IP lookups).

The callback has arguments (err, addresses). The type of each item in addresses is determined by the record type, and described in the documentation for the corresponding lookup methods below.

On error, err would be an instanceof Error object, where err.errno is one of the error codes listed below and err.message is a string describing the error in English.

dns.resolve4(domain, callback)

The same as dns.resolve(), but only for IPv4 queries (A records). addresses is an array of IPv4 addresses (e.g. ['', '', '']).

dns.resolve6(domain, callback)

The same as dns.resolve4() except for IPv6 queries (an AAAA query).

dns.resolveMx(domain, callback)

The same as dns.resolve(), but only for mail exchange queries (MX records).

addresses is an array of MX records, each with a priority and an exchange attribute (e.g. [{'priority': 10, 'exchange': ''},...]).

dns.resolveTxt(domain, callback)

The same as dns.resolve(), but only for text queries (TXT records). addresses is an array of the text records available for domain (e.g., ['v=spf1 ip4: ~all']).

dns.resolveSrv(domain, callback)

The same as dns.resolve(), but only for service records (SRV records). addresses is an array of the SRV records available for domain. Properties of SRV records are priority, weight, port, and name (e.g., [{'priority': 10, {'weight': 5, 'port': 21223, 'name': ''}, ...]).

dns.reverse(ip, callback)

Reverse resolves an ip address to an array of domain names.

The callback has arguments (err, domains).

If there an an error, err will be non-null and an instanceof the Error object.

Each DNS query can return an error code.


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

Tests if actual is equal to expected using the operator provided.

assert.ok(value, message)

Tests if value is a true value, 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.

assert.doesNotThrow(block, error, message)

Expects block not to throw an error.


This module contains utilities for dealing with file paths. Use require('path') to use it. It provides the following methods:

path.join(/ path1, path2, ... /)

Join all arguments together and resolve the resulting path. Example:

node> require('path').join('/foo', 'bar', 'baz/asdf', 'quux', '..')


Normalize an array of path parts, taking care of '..' and '.' parts. Example:

  'foo', 'bar', 'baz', 'asdf', 'quux', '..'])
// returns
[ '', 'foo', 'bar', 'baz', 'asdf' ]


Normalize a string path, taking care of '..' and '.' parts. Example:

// returns


Return the directory name of a path. Similar to the Unix dirname command. Example:

// returns

path.basename(p, ext)

Return the last portion of a path. Similar to the Unix basename command. Example:

// returns

path.basename('/foo/bar/baz/asdf/quux.html', '.html')
// returns


Return the extension of the path. Everything after the last '.', if there is no '.' then it returns an empty string. Examples:

// returns 

// returns

path.exists(p, callback)

Test whether or not the given path exists. Then, call the callback argument with either true or false. Example:

path.exists('/etc/passwd', function (exists) {
  sys.debug(exists ? 'it's there' : 'no passwd!');


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

Parsed URL objects have some or all of the following fields, depending on whether or not they exist in the URL string. Any parts that are not in the URL string will not be in the parsed object. Examples are shown for the URL


The following methods are provided by the URL module:

url.parse(urlStr, parseQueryString=false)

Take a URL string, and return an object. Pass true as the second argument to also parse the query string using the querystring module.


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

This module provides utilities for dealing with query strings. It provides the following methods:

querystring.stringify(obj, sep='&', eq='=')

Serialize an object to a query string. Optionally override the default separator and assignment characters. Example:

querystring.stringify({foo: 'bar'})
// returns

querystring.parse(str, sep='&', eq='=')

Deserialize a query string to an object. Optionally override the default separator and assignment characters.

// returns
{ 'a': 'b'
, 'b': 'c'


The escape function used by querystring.stringify, provided so that it could be overridden if necessary.


The unescape function used by querystring.parse, provided so that it could be overridden if necessary.


A Read-Eval-Print-Loop is available both as a standalone program and easily includable in other programs.

The standalone REPL is called node-repl and is installed at $PREFIX/bin/node-repl. It's recommended to use it with the program rlwrap for a better user interface. I set

alias node-repl='rlwrap node-repl'

in my zsh configuration.

Inside the REPL, Control+D will exit. The special variable _ (underscore) contains the result of the last expression.

The library is called /repl.js and it can be used like this:

var sys = require('sys'),
    net = require('net'),
   repl = require('repl');
nconnections = 0;
net.createServer(function (c) {
  nconnections += 1;
repl.start('simple tcp server> ');

The repl provides access to any variables in the global scope. You can expose a variable to the repl explicitly by assigning it to the repl.scope object:

var count = 5;
repl.scope.count = count;


Addons are dynamically linked shared objects. They can provide glue to C and C++ libraries. The API (at the moment) is rather complex, involving knowledge of several libraries:

Node statically compiles all its dependencies into the executable. When compiling your module, you don't need to worry about linking to any of these libraries.

To get started let's make a small Addon which does the following except in C++:

exports.hello = 'world';

To get started we create a file

#include <v8.h>

using namespace v8;

extern 'C' void
init (Handle<Object> target) 
  HandleScope scope;
  target->Set(String::New("hello"), String::New("World"));

This source code needs to be built into hello.node, the binary Addon. To do this we create a file called wscript which is python code and looks like this:

srcdir = '.'
blddir = 'build'
VERSION = '0.0.1'

def set_options(opt):

def configure(conf):

def build(bld):
  obj = bld.new_task_gen('cxx', 'shlib', 'node_addon') = 'hello'
  obj.source = ''

Running node-waf configure build will create a file build/default/hello.node which is our Addon.

node-waf is just[WAF], the python-based build system. node-waf is provided for the ease of users.

All Node addons must export a function called init with this signature:

extern 'C' void init (Handle<Object> target) 

For the moment, that is all the documentation on addons. Please see[node_postgres] for a real example.