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FreeSWITCH ESL Bindings for Node.js Build Status

A Library for handling low-level FreeSWITCH ESLconnections, and associated ESLevents.

Documentation - Event Socket Library Spec


Though there is already a Node.js "library" for this on github, it does not actually implement the Event Socket Library interface, and instead has it's own thing. This library was written to implement the full Event Socket Library interface, and provide a meaningful semantic when dealing with FreeSWITCH in Node.js.

This library supports both "Inbound" (connection going into FreeSWITCH) and "Outbound" (connections coming out of FreeSWITCH). Also included is a helper esl.Server object that manages multiple esl.Connection objects; making it trivial to have multiple "Outbound" connections from FreeSWITCH.


The easiest way to install is via npm:

npm install modesl

As in "Mod ESL".


The most basic usage example is to open a connection, and send a status command:

var esl = require('modesl'),
conn = new esl.Connection('', 8021, 'ClueCon', function() {
    conn.api('status', function(res) {
        //res is an esl.Event instance

Something to be aware of is that all functions that interact with FreeSWITCH are asynchronous on the Library side. However, there are many functions (api, execute, etc) that are synchronous on the FreeSWITCH side. Because of this the event you will get back in your callback on, for example, api and the same command on bgapi will be different.

The api command's callback will be executed immediately when the command/reply message is received, with all the returned data. However, that same command using bgapi will not call the callback when the command/reply message is received, this is because FreeSWITCH returns the command/reply message immediately for background commands before the command is run. The Library will automatically track the command, and call the callback on the BACKGROUND_JOB message that denotes a completed Background Job.

The body for the same command issued with api and bgapi should be the same; even when the headers, event type, and time it takes for the callback to execute are different. The Library attempts to smooth these differences out by providing a common interface, even though behind the scenes things are quite different.


To run the tests included with the module simply run the following in the root of the modesl folder:

npm test


  • Add tests for
  • esl.Connection
  • Add more examples for
  • IVR App
  • Faxing App
  • Add more abstraction/sugar functions
  • Better error messages on error event


This module is distributed under the Mozilla Public License 2.0.