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A port of the eSpeak speech synthesizer from C++ to JavaScript using Emscripten.

Enables text-to-speech on the web using only JavaScript and HTML5.


Very simple! Do this:

  • Include the script in your html header,

    <script src="speakClient.js"></script>

    (and make sure you have speakClient.js available, as well as speakWorker.js and speakGenerator.js)

  • Add a div with an audio element called 'audio' in your html body,

    <div id="audio"></div>

  • Call speak() to say stuff in JavaScript

    speak('hello world!')

See helloworld.html for a simple 'hello world', and demo.html for a more detailed example.


You can also specify some options with calling speak(), by doing

  `speak('hello world', { option1: value1, option2: value2 .. })`

available options are:

  • amplitude: How loud the voice will be (default: 100)
  • pitch: The voice pitch (default: 50)
  • speed: The speed at which to talk (words per minute) (default: 175)
  • voice: Which voice to use (for a non-default voice, requires you to build speak.js to include the proper data. See Language Support below) (default: en/en-us)
  • wordgap: Additional gap between words in 10 ms units (default: 0)
  • noWorker: Do not use a web worker (see below in 'Architecture')

For example

  `speak('hello world', { pitch: 100 })`

will talk in a very high-pitched voice.


speakClient.js is the file that you interact with. It defines speak(), and will load speakWorker.js in a web worker. speakWorker wraps around speakGenerator.js, which does the actual work of converting a string into a WAV file. The WAV data is returned to speak(), which then plays it in an HTML Audio element.

You can also use speak.js without a web worker. In that case, you don't need speakWorker.js, but you do need to load speakGenerator.js along with speakClient.js in your HTML page. speak(), if called with noWorker set to true in the options object, will directly call the WAV generation code in speakGenerator.js instead of forwarding the call to a worker which would have done the same.


A prebuilt version is already included. But if you want to tinker with the source code though, you might want to build it yourself. To do so, run inside src/. Note that you need to change the paths there.

Language Support

eSpeak supports multiple languages so speak.js can too. To do this, you need to build a custom version of speak.js:

  • Bundle the proper language files. For french, you need fr_dict and voices/fr. See commented-out code in and
  • Expose those files to the emulated filesystem, in post.js. See commented-out code in there as well.
  • Run to build.

You then need to call speak() with the voice option that tells it to use the right voice for your language. For example, for French this should work:

  `speak('boulanger', { voice: 'fr' })`