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node-webworkers is an implementation of the Web Workers API for node.js.

See the design document here.


Master source

var sys = require('sys');
var Worker = require('webworker');

var w = new Worker('foo.js');

w.onmessage = function(e) {
    sys.debug('Received mesage: ' + sys.inspect(e));

w.postMessage({ foo : 'bar' });

Worker source

onmessage = function(e) {
    postMessage({ test : 'this is a test' });

onclose = function() {
    sys.debug('Worker shuttting down.');


Supported API methods are

  • postMessage(e) in both workers and the parent; messages are in the parent if this is invoked before the child is fully initialized
  • onmessage(e) in both workers and the parent
  • onerror(e)in both workers and the parent
  • terminate() in the parent

In addition, some nonstandard APIs are provided

  • onclose() in the worker (allows for graceful shutdown)
  • The postMessage() method takes an additional optional file descriptor parameter, which will be sent with the message. This descriptor will be passed to onmessage handlers as an optional fd field. Handlers receiving messages posted without file descriptors will not see an fd field. Both the parent and child can send file descriptors using this mechanism.
  • Worker.onexit(code, signal) in the master, which is invoked on the master Worker object when the worker process exits.
  • The Worker constructor takes an additional optional object argument, opts, which is used as a dictionary of options with the following keys
    • args : A string or array of strings to pass to the executable before the filename to invoke. This can be used to request that the worker start up in debug mode (e.g. { 'args' : '--debug-brk' }). By default this is empty.
    • path : A string naming the executable to invoke for workers. By default this is the value of process.execPath (e.g. node or similar).


This package can be installed via npm as follows

% npm install webworker

Note that this requires node-websocket-client v0.9.3 or later. This dependency will be handled automatically by npm, but must be dealt with manually if installing using another procedure.


This package contains a static snapshot of Micheil Smith's excellent node-websocket-server with some fixes applied to handle UNIX sockets.


A WebWorkers implementation for NodeJS







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