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The Web MIDI API is a really exciting addition to the web platform that allows web developers to interact with MIDI musical instruments and devices. While great, most developers will find the Web MIDI API to be a bit too low-level for their needs. For example, sending and receiving MIDI messages involves performing binary arithmetic to encode or decode MIDI byte streams. Having to read the MIDI spec in order to properly do that is not fun. Also the native Web MIDI API makes it hard to react upon receiving MIDI messages from external devices. For example, it only allows a single callback function per channel. The goal behind WebMidi.js is to make all these things much easier.

Warning to users of version <= 1.x

The API in version 2.x has changed and is not backwards-compatible. Please check the Migration Notes below for more information.

Browser Support

This library works in all browsers that support the Web MIDI API. Currently, the following browsers have built-in support:

  • Chrome (Mac, GNU/Linux, Android & Windows)
  • Opera (Mac, GNU/Linux, Windows)
  • Android WebView component (KitKat and above)

It is possible to use this library in other browsers and in Node.js if you install version 1.4+ of Jazz-Plugin together with the WebMIDIAPIShim polyfill. This combination provides support for the following additional browsers:

  • Firefox (Mac, GNU/Linux & Windows)
  • Safari (Mac)
  • Internet Explorer (Windows)
  • Node.js (untested)

For details on how to use WebMidi.js with the Jazz-Plugin (and WebMIDIAPIShim, please skip ahead to the Using WebMidi.js with the Jazz-Plugin section.

Caveat Emptor

WebMidi.js v2 is currently in the release candidate stage. The API should now be stable and most bugs should have been ironed out. However, until it reaches the final stage, it cannot be considered production-ready. If you find a bug, please open an issue and I will do my best to address it in a timely fashion.

Having confirmation that the software works well is also valuable information. If that's the case for you, please drop me a note at @jpcote.


Depending on your needs and environment, you can install WebMidi.js in one of three ways: manually, with Bower or with NPM.

Manual Install

You can install WebMidi.js the old fashioned way by downloading the latest release packaged as a zip file. Uncompress the package, grab the webmidi.min.js file and copy it to your project. Link to it from your HTML page as usual.

Bower Install

To install via Bower, simply run the following command in the Terminal (Mac, Linux) or the Command Prompt (Windows) from the root of your project. Just make sure to correctly capitalize the "W" and the "M" in "WebMidi":

bower install WebMidi

Then, just add a <script> tag to your HTML page and make it point to:

<script src="bower_components/WebMidi/src/webmidi.js"></script>

NPM Install

If you prefer, you can install WebMidi.js with NPM. Simply issue the following command to perform the actual install:

npm install webmidi

Finally, just add a <script> tag to your HTML page and make it point to:

<script src="node_modules/webmidi/webmidi.min.js"></script>

Quick Start

Getting started is easy. The first thing to do is to enable WebMidi.js. To do that, you call WebMidi.enable() and pass it a function to execute when done. This function will receive an Error object if enabling WebMidi failed:

WebMidi.enable(function (err) {
  if (err) {
    console.log("WebMidi could not be enabled.", err);
  } else {
    console.log("WebMidi enabled!");

If you need sysex support, you will have to pass true as the second parameter to the enable() function.

To send and receive MIDI messages, you will need to do so via the appropriate Output and Input device. To view all the available Input and Output ports, you can use the matching arrays:

WebMidi.enable(function (err) {

To send MIDI messages to a device, you simply need to grab that device and call one of its output method (playNote(), stopNote(), sendPitchBend(), etc.). To retrieve a device, you can can use its position in the WebMidi.outputs array. For instance, to grab the first output device, you could use:

var output = WebMidi.outputs[0];

However, this is not very safe as the position of devices in the array could change. An alternative is to use the device's ID:

var output = WebMidi.getOutputById("1584982307");

Beware that device IDs are not the same accross browsers and platforms. You could also use the device's name (as displayed in the WebMidi.outputs array):

var output = WebMidi.getOutputByName("Axiom Pro 25 Ext Out");

Then, you can call any of the output methods and all native MIDI communications will be handled for you. For example, to play a "C" on the 3rd octave, you simply do:


That's it.

Receiving messages works in a similar way: you retrieve the Input device you want to use, and then add a callback function to be triggered when a specific MIDI message is received. For example, to listen for pitch bend events on all channels of the device:

var input = WebMidi.getInputByName("Axiom Pro 25 USB A In");
input.addListener('pitchbend', "all", function(e) {
    console.log("Pitch value: " + e.value);

More code examples

Here are various other examples to give you an idea of what is possible with WebMidi.js. For all details, please consult the full API documentation.

// Enable WebMidi.js 
WebMidi.enable(function (err) {
  if (err) {
    console.log("WebMidi could not be enabled.", err);
  // Viewing available inputs and outputs 
  // Display the current time 
  // Retrieving an output port/device using its id, name or index 
  var output = WebMidi.getOutputById("123456789");
  output = WebMidi.getOutputByName("Axiom Pro 25 Ext Out");
  output = WebMidi.outputs[0];
  // Play a note on all channels of the selected output 
  // Play a note on channel 3 
  output.playNote("Gb4", 3);
  // Play a chord on all available channels 
  output.playNote(["C3", "D#3", "G3"]);
  // Play a chord on channel 7 
  output.playNote(["C3", "D#3", "G3"], 7);
  // Play a note at full velocity on all channels) 
  output.playNote("F#-1", "all", {velocity: 1});
  // Play a note on channel 16 in 2 seconds (relative time) 
  output.playNote("F5", 16, {time: "+2000"});
  // Play a note on channel 1 at an absolute time in the future 
  output.playNote("F5", 16, {time: WebMidi.time + 3000});
  // Play a note for a duration of 2 seconds (will send a note off message in 2 seconds). Also use 
  // a low attack velocity 
  output.playNote("Gb2", 10, {duration: 2000, velocity: 0.25});
  // Stop a playing note on all channels 
  // Stopping a playing note on channel 11 
  output.stopNote("F3", 11);
  // Stop a playing note on channel 11 and use a high release velocity 
  output.stopNote("G8", 11, {velocity: 0.9});
  // Stopping a playing note in 2.5 seconds 
  output.stopNote("Bb2", 11, {time: "+2500"});
  // Send polyphonic aftertouch message to channel 8 
  output.sendKeyAftertouch("C#3", 8, 0.25);
  // Send pitch bend (between -1 and 1) to channel 12 
  output.sendPitchBend(-1, 12);
  // You can chain most method calls 
  output.playNote("G5", 12)
    .sendPitchBend(-0.5, 12, {time: 400}) // After 400 ms. 
    .sendPitchBend(0.5, 12, {time: 800})  // After 800 ms. 
    .stopNote("G5", 12, {time: 1200});    // After 1.2 s. 
  // Retrieve an input by name, id or index 
  var input = WebMidi.getInputByName("nanoKEY2 KEYBOARD");
  input = WebMidi.getInputById("1809568182");
  input = WebMidi.inputs[0];
  // Listen for a 'note on' message on all channels 
  input.addListener('noteon', "all",
    function (e) {
      console.log("Received 'noteon' message (" + + e.note.octave + ").");
  // Listen to pitch bend message on channel 3 
  input.addListener('pitchbend', 3,
    function (e) {
      console.log("Received 'pitchbend' message.", e);
  // Listen to control change message on all channels 
  input.addListener('controlchange', "all",
    function (e) {
      console.log("Received 'controlchange' message.", e);
  // Check for the presence of an event listener (n such cases, you cannot use anonymous functions). 
  function test(e) { console.log(e); }
  input.addListener('programchange', 12, test);
  console.log("Has event listener: ", input.hasListener('programchange', 12, test));
  // Remove a specific listener 
  input.removeListener('programchange', 12, test);
  console.log("Has event listener: ", input.hasListener('programchange', 12, test));
  // Remove all listeners of a specific type on a specific channel 
  input.removeListener('noteoff', 12);
  // Remove all listeners for 'noteoff' on all channels 
  // Remove all listeners on the input 

Full API Documentation

The full API documentation is available for download in the docs folder. You can also view it online.

Legacy documentation for version 1.0.0-beta.15 will also remain available online as long as necessary.

Migration Notes

If you are upgrading from version 1.x to 2.x, you should know that v2.x is not backwards compatible. Some important changes were made to the API to make it easier to use, more versatile and to better future-proof it.

Here is a summary of the changes:

  • All the "output" functions (playNote(), sendPitchBend(), etc.) have been moved to the Output object. A list of all available Output objects is available in WebMidi.outputs (like before).

  • All the "input" functions (addListener, removeListener() and hasListener() have been moved to the Input object. A list of all available Input objects is available in WebMidi.inputs (also like before).

There might be a few other minor changes here and there but the refactoring mostly concerns the introduction of Input and Output objects.

Using WebMidi.js with the Jazz-Plugin

To use WebMidi.js on Safari, Firefox and Internet Explorer, you will first need to install Jazz-Plugin. Simply download the plugin and run the installer.

Then, you will need to add the plugin to the page with the following HTML code:

<object id="Jazz1" classid="CLSID:1ACE1618-1C7D-4561-AEE1-34842AA85E90" class="hidden">
  <object id="Jazz2" type="audio/x-jazz" class="hidden">
    <p><a href=>Jazz-Plugin</a> required!</p>

To support recent versions of Internet Explorer, you also need to add a meta tag to the <head> of the page:

<meta http-equiv="X-UA-Compatible" content="requiresActiveX=true"/>

Since Jazz-Plugin does not use the same syntax as the native Web MIDI API, it is necessary to also install the WebMIDIAPIShim polyfill. You can do that by including the following in your page:

<script src=''></script>

Obviously, you can also download a local copy and link to it.

Support the Project

If you find this library useful, you can buy me a drink as a token of your appreciation. This would automatically make you even more awesome than you already are!