Skip to content


Subversion checkout URL

You can clone with
Download ZIP
Node.js client and server for FreeSwitch Event Socket


latest commit ed4b8548db
@shimaore authored

This module is a promise-based, chainable, client ('inbound' event socket) and server ('outbound' event socket) for FreeSwitch, written entirely in Javascript with no dependencies on the libesl library. This module is actively maintained and used in production systems.

Client Usage

The following code does the equivalent of fs_cli -x: it connects to the Event Socket, runs a single command, then disconnects.

FS = require('esl');

var fs_command = function(cmd) {

  var client = FS.client(function(){
    .then( function(res) {
      // res contains the headers and body of FreeSwitch's response.
    .then( function(){
    .then( function(){



The API methods return promises.

The original example as CoffeeScript:

FS = require 'esl'

fs_command = (cmd) ->

  client = FS.client ->
    @api cmd
    .then -> @exit()
    .then -> client.end()

  client.connect 8021, ''

fs_command 'reloadxml'

Server Usage

From the FreeSwitch XML dialplan, you can connect to an Event Socket server using for example:

<action application="set" data="socket_resume=true"/>
<action application="socket" data=" async full"/>
<action application="respond" data="500 socket failure"/>

Here is a simplistic event server:

var call_handler = function() {
  .command('play-file', 'voicemail/vm-hello')
  .then(function(res) {
     var foo = res.body.variable_foo;
  .hangup() // hang-up the call
  .exit()   // tell FreeSwitch we're disconnecting


Message tracing

During development it is often useful to be able to see what messages are sent to FreeSwitch or received from FreeSwitch. This module uses the debug module for tracing; simply call your application with


to see traces.

The names available are esl:response and esl:main.


npm install esl

Examples and Documentation

The test suite in test/ provides many examples.

The methods available inside the call-handler are those of the response object: queue_api, api, bgapi, command, command_uuid, etc.


This module is modelled after Node.js' own httpServer and client, and uses an event-driven interface wrapper inside a promise-based API.

It offers two Event Socket handlers, client() and server().

Typically a client would be used to trigger calls asynchronously (for example in a click-to-dial application); this mode of operation is called "inbound" (to FreeSwitch) in the Event Socket FreeSwitch documentation.

A server will handle calls sent to it using the "socket" diaplan application (called "outbound" mode in the Event Socket Outbound FreeSwitch documentation). The server is available at a pre-defined port which the socket dialplan application will specify.


Please use GitHub issues.

Client Notes

Note: Use call.event_json 'HEARTBEAT' to start receiving event notifications.

Server Notes

For some applications you might want to capture channel events instead of using the command() / callback pattern:

var esl = require('esl'),
    util = require('util');

var call_handler = function() {

  # for debugging

  # These are called asynchronously.
  this.once('CHANNEL_ANSWER').then( function () {
    util.log('Call was answered');
  this.once('CHANNEL_HANGUP').then(  function () {
    util.log('Call hangup');
  this.once('CHANNEL_HANGUP_COMPLETE').then(  function () {
    util.log('Call was disconnected');
  # However note that `on` cannot use a Promise (since it only would
  # get resolved once).
  this.on('SOME_MESSAGE', function(call) {
    util.log('Got Some Message');

var server = esl.server(call_handler)


The present module should be more convenient if you've already coded for Node.js and are used to promises and events. If you are coming from the world of FreeSwitch and are used to the Event Socket Library API, you might want to try node-esl.

Projects using this module

  • tough-rate is a dynamic LCR engine for FreeSwitch that uses a middleware stack to process calls.
  • useful-wind is a middleware-based framework for FreeSwitch call-handling. (Think of it as ExpressJS for FreeSwitch.)
Something went wrong with that request. Please try again.