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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.

Build Status

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(){
    var res = await this.api(cmd)
    // res contains the headers and body of FreeSwitch's response.
    await this.exit();



The API methods return promises.

The original example as CoffeeScript:

FS = require 'esl'

fs_command = (cmd) ->

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

  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() {
  res = await this.command('play-file', 'voicemail/vm-hello')
  var foo = res.body.variable_foo;
  await this.hangup() // hang-up the call
  await this.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 API provides a summary of usage.

The methods available inside the call-handler are those of the response object: 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('CHANNEL_HANGUP_COMPLETE','DTMF') 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.onceAsync('CHANNEL_ANSWER').then( function () {
    util.log('Call was answered');
  this.onceAsync('CHANNEL_HANGUP').then(  function () {
    util.log('Call hangup');
  this.onceAsync('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');
  // Remember to accept the messages since we're using `all_events: false` below.

var server = esl.server({all_events:false},call_handler)

Migrating from earlier versions

  • once has been renamed to onceAsync; onceAsync(event) returns a Promise. once is now the regular event-emitter once(event,callback).
  • Promises are native Promises, not bluebird's.


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.


Node.js client and server for FreeSwitch Event Socket





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