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dy.js reloader

This is a live-reloading system designed to function as both a helpful development tool and a reference implementation for extending the dy.js specification.


Firstly, refer to the example/ sample project for usage.

The reloader library is currently designed to work with express. You simply bind it to your server like so:

// app.js

// setting up your express application
app = express()

var server = app.listen(3000)
// Setup a reloader sub-server on the application and its server
var reloader = new dy.Reloader(app, server)
reloader.addReloadable(new dy.Reloadable('example', {
  watch: './public/js/example.js',
  reload: '/js/example.js'

This assumes you have a dy.js module defined in public/js/example.js:

// public/js/example.js
dy('example', [], function () {

  this._load = function () {
    // This will be executed every time the module is loaded
    var el = document.getElementById('main')
    el.innerText = 'Hello from example at '+(new Date()).getTime()
  this._unload = function () {
    // This will be called when the module is unloaded
    var el = document.getElementById('main')
    el.innerText = 'example: Unloaded'


Then in your HTML you would setup dy.js and the reloader:

<!-- index.html -->

<!-- from public/js/ -->
<script type="text/javascript" src="/js/dy.js"></script>
<script type="text/javascript" src="/js/example.js"></script>
<!-- from dy.Reloader -->
<script type="text/javascript" src="/.dy/browser.js"></script>
<!-- setup -->
<script type="text/javascript">
window.onload = function () {
  var reloader = new dy.Reloader(dy)

<div id="main">Hello from the HTML</div>

Now every time public/js/example.js is changed it will be reloaded in the browser. In detail the process looks like:

  1. The dy.Reloader adds itself to the Node express server
  2. The dy.Reloader in the browser does GET /.dy/reloadables.json to the server library to get a manifest of modules it should reload (this is set up when you call reloader.addReloadable on the server library)
  3. The server library watches reloadable files for changes
  4. When it detects a change it sends a message to the browser through the /.dy/primus websocket
  5. The browser receives the message and creates a new <script> tag with the correct file to load, adds an onload handler to it, and then injects it into the DOM
  6. The browser loads the source of the <script> tag (which is the new module); the dy('example' ...) call in that source file updates the definition of the example module in the browser's dy manager
  7. When the browser is done loading that <script> tag it calls the onload handler; that handler then fires the _load() trigger on the now-reloaded module
  8. The _load() trigger on the example module updates the "Hello from example ..." text in the DOM.