The Squash client library for JavaScript front-end projects.
JavaScript Ruby CSS HTML

Squash Client Library: JavaScript

This client library reports front-end JavaScript exceptions to Squash, the Squarish exception reporting and management system.


For an overview of the various components of Squash, see the website documentation at

JavaScript client

Documentation is written in Codo format. HTML documentation can be generated by running rake doc:js. Note that Codo is still a work in progress, and the generated docs will have some formatting errors. The documentation is written to the doc/js directory.

If you do not have Codo installed in your path, you can download a project-local install with rake setup.

Ruby library

Markdown-formatted YARD documentation is available by running rake doc:ruby. The documentation is written to the doc/ruby directory.


The JavaScript library is compatible with any modern JavaScript engine, including any version of V8, Nitro, and Chakra.

The Rails engine (allowing the library to be easily used in a Rails app) is compatible with Rails 3.1 and later.


The JavaScript library uses TraceKit for cross-platform stack trace extraction. The library is included in this project. For Rails projects, a Sprockets include file is provided. For non-Rails projects, the output of rake minify rolls in the library.

The included version of TraceKit has been modified somewhat:

  • window.onerror support was expanded to include changes in recent versions of modern browsers (namely, passing the column and error object as parameters).
  • TraceKit was causing unexpected behavior on Chrome and Firefox, and parts of it are commented out. (The jQuery hooks were disabled.)



For Rails applications, add the Squash client engine to your Gemfile with gem 'squash_javascript', require: 'squash/javascript', and then include the JavaScript into your application.js file (or other JavaScript manifest):

//= require squash_javascript

Other projects

For other projects, you may need to compile the CoffeeScript file first. If you do not have the coffee binary installed in your path, you can download and install a copy of CoffeeScript by running rake setup. This task uses npm (the Node package manager) to perform the installation; you will need to install npm first if you haven't already. CoffeeScript will be installed into a project-local directory.

Once you have the coffee binary, you can run rake minify to generate a JavaScript file that you can use in your project. If you would like a non-minified JavaScript file without dependencies, run rake compile.

Place the compiled squash_javascript.min.js file in a Web-public directory and include it using a <script> tag:

<script type="text/javascript" href="" />

The file defines a SquashJavascript singleton which is accessible using SquashJavascript.instance().

Configuring CORS

In order for applications to report their JavaScript errors to Squash, your Squash instance must be configured to accept cross-origin requests from your other website. In your Squash web code, update the allowed_origins configuration (under config/environments/[environment]/dogfood.yml) to include the host serving your application.


Before you can use Squash, you must configure it (see Configuration below). At a minimum, you must specify

  • the host on which Squash is running,
  • your project's API key,
  • the environment, and
  • the SHA of the Git revision currently deployed.

Use SquashJavascript.instance().configure to set up the Squash JavaScript client:

SquashJavascript.instance().configure({APIHost: 'YOUR_API_HOST',
                                   APIKey: 'YOUR_API_KEY',
                                   environment: 'production',
                                   revision: '8718e4336990f9ea0198c2ff5668bbb673befd65'})

Squash will automatically install a listener that will trap exceptions, send them to the server, and re-throw them. Note that the client will only notify for instances of the Error class.

There are many additional features you can take advantage of; see Additional Features below.

Additional Features

There are a number of other features you can take advantage of to help you debug your exceptions:

User Data

Exceptions can be annotated with freeform user data. This data can take any format and have any meaning, typically being relevant to the exception at hand.

There are multiple ways to add user data to an exception. The most straightforward way is to include the user data as the second argument to the notify method:

SquashJavascript.instance().notify(error, {event: e, arguments: arguments});

You can apply user data to a block of code using the SquashJavascript.instance().addUserData method:

$(window).resize(function(e) {
  SquashJavascript.instance().addUserData({event: e}, function() {
    // ... process event ...

If that's too verbose, there's additionally a curry function, addingUserData, that takes a function, applies the addUserData behavior to it, and returns a new function:

$(window).resize(SquashJavascript.instance().addingUserData({event: e}, function(e) {
  // ... process event ...

And lastly, you can add user data directly to the exception:

function myFunction(value) {
  if (value < 0) {
    var err = new Error("value was less than 0");
    err._squash_user_data = { value: value };
    throw err;

  // ... do the thing ...

You can also add user data to exceptions you catch and re-throw:

try {
} catch (err) {
  if (!err._squash_user_data) err._squash_user_data = new Object();
  err._squash_user_data.input = input;
  throw err; // assumed that SquashJavascript.instance().notify is called somewhere further up in the stack

Ignoring Exceptions

You can ignore certain error classes within a block of code if those exceptions are not worth sending to Squash. Use the SquashJavascript.instance().ignore_exceptions method:

SquashJavascript.instance().ignoreExceptions(EvalError, SyntaxError, function() {
  // ... some code ...

The curry-type syntax is also supported here:

$(window).resize(SquashJavascript.instance().ignoringExceptions(EvalError, SyntaxError, function(e) {
  /// ... some code ...

The exceptions will be raised (not eaten) but will not be reported to Squash.

You can also globally ignore exceptions using the ignored_exceptions configuration; see Configuration below.


You can configure the client with the SquashJavascript.instance().configure method. Calling this method multiple times will merge new values in with the existing configuration. The method takes a hash, which accepts the following keys:


  • disabled: If true, the Squash client will not report any errors.
  • APIKey: The API key of the project that exceptions will be associated with. This configuration option is required. The value can be found by going to the project's home page on Squash.
  • environment: The environment that exceptions will be associated with. This configuration option is required.
  • revision: The SHA1 of the current Git revision. This is the revision of the code that is currently running. This configuration option is required.

Error Transmission

  • APIHost: The host on which Squash is running. Required.
  • notifyPath: The path to post new exception notifications to. By default it's set to /api/1.0/notify.
  • transmitTimeout: The amount of time to wait before giving up on trasmitting an error. By default this is treated as both an open and a read timeout.

Ignored Exceptions

  • ignoredExceptionClasses: An array of exception class names that will not be reported to Squash.
  • ignoredExceptionMessages: A hash mapping an exception class name to an array of regexes. Exceptions of that class whose messages match a regex in the list will not be reported to Squash.

Error Transmission

Exceptions are transmitted to Squash using JSON-over-XMLHttpRequest. A default API endpoint is pre-configured, though you can always set your own (see Configuration above).

Failsafe Reporting

In the event that the Squash client itself raises an exception when processing an exception, it will log that exception to the console. Both the original exception and the failsafe error will be logged. The original exception will still be re-raised, but the failsafe error will be "eaten."

Source Mapping

Rails and Sprockets

Squash JavaScript can integrate with Sprockets to automatically generate source maps for each stage of the asset compilation pipeline, then integrate with Capistrano to upload the source maps to Squash. To use this feature, configure your project like so:

  1. Replace your JavaScript compiler gem with Closure, if you aren't already using it.

    -gem 'uglifier'
    +gem 'closure-compiler'
  2. Use Squash's source-mapping Tilt engines for CoffeeScript and JavaScript.

    These Tilt engines wrap existing Tilt template engines, but also generate source maps to tmp/sourcemaps.

    Sprockets.register_engine '.coffee', Squash::Javascript::SourceMappingCoffeescriptTemplate
    config.assets.js_compressor = Squash::Javascript::SourceMappingJavascriptMinifier
  3. Add the Squash Capistrano tasks to your Capfile:

    require 'squash/javascript/capistrano'

    If you do not use Capistrano 3, you can use the rake sourcemaps:upload:all task to upload your generated source maps to Squash.

Other Projects

If you can generate a source map for your minified JavaScript files (Closure can), you can use this gem to upload that source map to Squash, where it will be used to convert minified stack traces to their original format, which can then benefit from Git-blaming, context, and other features of Squash.

To upload the source map to squash, run the upload_source_map binary included with this gem, and pass it four arguments: 1) your Squash host, 2) your API key, 3) the environment name, and 4) the path to the JSON source map. Example:

upload_source_map abc-123-abc-123-abc-123 production artifacts/mapping.json

Use --help to learn about additional options.


JavaScript client

Jasmine unit and integration tests are implemented in the spec/js directory. To run these tests, run rake spec:js (Mac OS X required), or simply compile the CoffeeScript source and open the SpecRunner.html file in your favorite Web browser.

Ruby library

RSpec unit tests are implemented in the spec/ruby directory. To run these tests, run rake spec:ruby.