laithshadeed / boomerang

End user oriented web performance testing and beaconing

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  • Copyright (c) 2011, Yahoo! Inc. All rights reserved.
  • Copyright (c) 2011-2012, Log-Normal Inc. All rights reserved.
  • Copyright (c) 2012-2017 SOASTA, Inc. All rights reserved.
  • Copyright (c) 2017, Akamai Technologies, Inc. All rights reserved.
  • Copyrights licensed under the BSD License. See the accompanying LICENSE.txt file for terms.

boomerang always comes back, except when it hits something.


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boomerang is a JavaScript library that measures the page load time experienced by real users, commonly called RUM (Real User Measurement). It has the ability to send this data back to your server for further analysis. With boomerang, you find out exactly how fast your users think your site is.

Apart from page load time, boomerang measures performance timings, metrics and characteristics of your user's web browsing experience. All you have to do is include it in your web pages and call the BOOMR.init() method. Once the performance data is captured, it will be beaconed to your chosen URL.

boomerang is designed to be a performant and flexible library that can be adapted to your site's needs. It has an extensive plugin architecture, and works with both traditional and modern websites (including Single Page Apps).

boomerang's goal is to not affect the load time of the page (avoiding the Observer Effect). It can be loaded in an asynchronous way that will not delay the page load even if boomerang.js is unavailable.


  • Supports:
    • IE 6+, Edge, all major versions of Firefox, Chrome, Opera, and Safari
    • Desktop and mobile devices
  • Captures (all optional):
    • Page characteristics such as the URL and Referrer
    • Overall page load times (via NavigationTiming if available)
    • DNS, TCP, Request and Response timings (via NavigationTiming)
    • Browser characteristics such as screen size, orientation, memory usage, visibility state
    • DOM characteristics such as the number of nodes, HTML length, number of images, scripts, etc
    • ResourceTiming data (to reconstruct the page's Waterfall)
    • Bandwidth
    • Mobile connection data
    • DNS latency
    • JavaScript Errors
    • XMLHttpRequest instrumentation
    • Third-Party analytics providers IDs
    • Single Page App interactions


boomerang can be included on your page in one of two ways: synchronously or asynchronously.

The asynchronous method is recommended.

The simple synchronous way

<script src="boomerang.js"></script>
<script src="plugins/rt.js"></script>
<!-- any other plugins you want to include -->
    beacon_url: ""

Note: You must include at least one plugin (it doesn't have to be RT) or else the beacon will never fire.

Each plugin has its own configuration as well -- these configuration options should be included in the BOOMR.init() call:

  beacon_url: "",
  ResourceTiming: {
    enabled: true,
    clearOnBeacon: true

The faster, more involved, asynchronous way

Loading boomerang asynchronously ensures that even if boomerang.js is unavailable (or loads slowly), your host page will not be affected.

1. Add a plugin to init your code

Create a plugin (or use the sample zzz-last-plugin.js) with a call to BOOMR.init:

  config: parameters,
BOOMR.t_end = new Date().getTime();

You could also include any other code you need. For example, you could include a timer to measure when boomerang has finished loading (as above).

2. Build boomerang

The build process bundles boomerang.js and all of the plugins listed in plugins.json (in that order).

To build boomerang with all of your desired plugins, you would run:

grunt clean build

This creates a deployable boomerang in the build directory, e.g. build/boomerang-<version>.min.js.

Install this file on your web server or origin server where your CDN can pick it up. Set a far future max-age header for it. This file will never change.

3. Asynchronously include the script on your page

There are two methods of asynchronously including boomerang on your page: by adding it to your main document, or via an IFRAME.

The former method could block your onload event (affecting the measured performance of your page), so the later method is recommended.

3.1. Adding it to the main document

Include the following code at the top of your HTML document:

(function(d, s) {
  var js = d.createElement(s),
      sc = d.getElementsByTagName(s)[0];

  sc.parentNode.insertBefore(js, sc);
}(document, "script"));

Best practices will suggest including all scripts at the bottom of your page. However, that only applies to scripts that block downloading of other resources.

Including a script this way will not block other resources, however it will block onload.

Including the script at the top of your page gives it a good chance of loading before the rest of your page does, thereby reducing the probability of it blocking the onload event.

If you don't want to block onload either, use the following IFRAME method:

3.2. Adding it via an IFRAME

The method described in 3.1 will still block onload on most browsers.

To avoid blocking onload, we can load boomerang in an asynchronous IFRAME. The general process is documented on in this blog post.

For boomerang, the asynchronous loader snippet you'll use is:

  // Boomerang Loader Snippet version 10
  if (window.BOOMR && (window.BOOMR.version || window.BOOMR.snippetExecuted)) {

  window.BOOMR = window.BOOMR || {};
  window.BOOMR.snippetExecuted = true;

  var dom, doc, where, iframe = document.createElement("iframe"), win = window;

  function boomerangSaveLoadTime(e) {
    win.BOOMR_onload = (e && e.timeStamp) || new Date().getTime();

  if (win.addEventListener) {
    win.addEventListener("load", boomerangSaveLoadTime, false);
  } else if (win.attachEvent) {
    win.attachEvent("onload", boomerangSaveLoadTime);

  iframe.src = "javascript:void(0)";
  iframe.title = "";
  iframe.role = "presentation";
  (iframe.frameElement || iframe).style.cssText = "width:0;height:0;border:0;display:none;";
  where = document.getElementsByTagName("script")[0];
  where.parentNode.insertBefore(iframe, where);

  try {
    doc = iframe.contentWindow.document;
  } catch (e) {
    dom = document.domain;
    iframe.src = "javascript:var;d.domain='" + dom + "';void(0);";
    doc = iframe.contentWindow.document;
  } = function() {
    var js = this.createElement("script");
    if (dom) {
      this.domain = dom;
    } = "boomr-if-as";
    js.src = '<version>.js';
    BOOMR_lstart = new Date().getTime();
  doc.write('<bo' + 'dy onload="document._l();">');

The id of the script node created by this code MUST be boomr-if-as as boomerang looks for that id to determine if it's running within an IFRAME or not.

boomerang will still export the BOOMR object to the parent window if running inside an IFRAME, so the rest of your code should remain unchanged.

3.3. Identifying when boomerang has loaded

If you load boomerang asynchronously, there's some uncertainty in when boomerang has completed loading. To get around this, you can subscribe to the onBoomerangLoaded Custom Event on the document object:

// Modern browsers
if (document.addEventListener) {
  document.addEventListener("onBoomerangLoaded", function(e) {
    // e.detail.BOOMR is a reference to the BOOMR global object
// IE 6, 7, 8 we use onPropertyChange and look for propertyName === "onBoomerangLoaded"
else if (document.attachEvent) {
  document.attachEvent("onpropertychange", function(e) {
    if (!e) e=event;
    if (e.propertyName === "onBoomerangLoaded") {
      // e.detail.BOOMR is a reference to the BOOMR global object

Note that this only works on browsers that support the CustomEvent interface, which is Chrome (including Android), Firefox 6+ (including Android), Opera (including Android, but not Opera Mini), Safari (including iOS), IE 6+ (but see the code above for the special way to listen for the event on IE6, 7 & 8).

boomerang also fires the onBeforeBoomerangBeacon and onBoomerangBeacon events just before and during beaconing.


Documentation is in the docs/ directory. Boomerang documentation is written in Markdown and is built via JSDoc.

You can build the current documentation by running Grunt:

grunt jsdoc

HTML files will be built under build/docs.

Open-source Boomerang Documentation is currently published at

The team at Akamai works on mPulse Boomerang, which contains a few mPulse-specific plugins and may have additional changes being tested before being backported to the open-source Boomerang. mPulse Boomerang usage documentation is available at and mPulse Boomerang API documentation is at

Additional documentation:

Source code

The boomerang source code is primarily on GitHub at

Feel free to fork it and contribute to it.

You can also get a check out the releases or download a tarball or zip of the code.


We use GitHub Issues for discussions, feature requests and bug reports.

Get in touch at

boomerang is supported by the developers at Akamai, and the awesome community of open-source developers that use and hack it. That's you. Thank you!


Boomerang is brought to you by:

To help out, please read our contributing page.


End user oriented web performance testing and beaconing



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