closure compiler externs for underscore 1.4.4

Closure Compiler externs for underscore 1.4.4 are now available.

Underscore 1.4.4 adds two new functions, _.findWhere, and _.partial.

Also pushed some fixes to 1.4.3 externs:

  • typo in `properties` param for _.where
  • a bunch of methods should be able to operate on Arguments objects as well as Arrays. Previously, only Arrays were noted as valid params by the externs.

Simplify QAing the js popup windows in your web app

QAing js popup windows in your web app is a pain in the ass. It’s easy to miss windows in obscure corners of your UI and can be hard to recreate the circumstances under which they’re shown, and the various states that determine how and when they appear. Automated js tests with a library like Qunit or Jasmine, while great, don’t really help when you need to make sure things look a certain way.

Fortunately, if you make a couple assumptions that I think hold true for a majority of web apps, we can simplify this testing process substantially.

Closure Compiler externs updates

Just pushed fixes and updates to my Closer Compiler externs for underscore, and created a repo for Qunit externs (which is probably not of any use to anyone, but is used by for testing accuracy/completeness of underscore externs).


  • Externs for latest underscore (1.4.3).
  • Some fixes to 1.3.3 externs, indicating that more methods may return wrapped objects (this is still incomplete).
  • Tests for externs file completeness/accuracy by running underscore’s own qunit tests through closure compiler. The output (using advanced compilation) is nasty and contains a lot of errors, but most of them are irrelevant. Some do point to legitimate issues, mostly related to uncommon ways of passing arguments to various methods.


  • Externs missing for `throws`, callbacks, and configuration. Mostly complete.

Exploring Chrome’s timeline panel

Subsequent to some performance issues with a few Backbone apps, I spent some time digging further into Google Chrome’s timeline panel, and specifically the memory view that shows allocated memory, and breaks down the number of DOM nodes held in memory.

Some tests/demos along with provisional findings are provided here: chrome timeline exploration. The official documentation for Chrome’s dev tools is getting better, but could still use improvement. Hopefully this will go some way to providing a bit more insight into what’s going on, what different numbers mean, and what sort of behaviour you can expect from common scenarios.

As I’m nowhere near an expert of Chrome’s internals nor on memory profiling in general, any suggestions or corrections are more than welcome (pull requests or whatever).

Avoiding 503s when loading images from Google Contacts API

There’s a variety of mildly annoying things about V3 of Google’s Contacts API (lack of control over which fields are returned, basically non-existent sorting ability, use of oauth bearer tokens; also they seem to be confused about their supposed mitigation of the confused deputy problem: validation does not actually seem to be required, nor does this in any way prevent an attacker from stealing the token and doing whatever they like with it).

One of the most annoying “features” is the undocumented rate limit when requesting images for a user’s contacts, each request of which must be authenticated. The rate limit appears to be around 10/s.

I wrote a lightweight jQuery plugin that will help you avoid the 503 errors that Google’s API returns when you begin exceeding this limit.

jQuery batched image loader

The github page has basic implementation details.

Scrolling while paused in Chrome debugger

If you’ve spent much time with Chrome’s debugger, you’ve probably encountered a few annoying scenarios, in which the locked-up view of the web page you’re working on prevents you from inspecting elements or scrolling.

An easy workaround for the scrolling lock-up is to just jump to the console, and:

window.scrollTo(0, 800)

Backbone.js finite state machine view

I developed a basic Backbone.js finite state machine (FSM) view for use on a project I was working on a while ago, and have been meaning to clean up the code and share it for a while now. It is now available on github, along with some qunit and sinon tests.

It was written to handle complex form navigation, i.e. when you want to conditionally guide a user through a path of form fields depending on their previous answers, and so while it could perhaps be shoehorned into other uses, this is where it will be the most natural fit. It works basically by binding a method to the change event on form fields that translates this event into terms understood by the FSM, and then calls transitions that you’ve defined when initializing the view.

There is some basic js and HTML on the github page demonstrating use. I plan to have more/better code, along with a working example, at some point.


Since writing this a few other people have come up with implementations that, though they appear quite different from mine, would accomplish mostly the same thing. See backbone.statemachine, and machina.js. Also, I definitely got inspiration for this code from a few other places on the web while writing it, but can’t track them down now. If anyone reading this thinks it reminds them of something they’ve seen elsewhere, or if they have suggestions on how it could be improved, feel free to let me know. I’m always open to suggestions and/or pull requests.

Closure compiler externs files for underscore and backbone js

As part of some other things I’m working on I’ve begun building upon some existing closure compiler externs files for the Underscore and Backbone js libraries. Both are still in quite early stages, but if you need something like this, they’re currently better than nothing.

backbone-js-externs on github, for Backbone 0.9.2

underscore-js-externs on github, for Underscore 1.3.3

The Backbone externs file is taken from this gist, which was autogenerated by DotNetWise’s externs extractor. It does a decent but very basic job.

The Underscore externs file is taken from the official Closure Compiler repository. The only changes I’ve made so far are

  • fixing a type annotation for the _.uniq and _.unique functions that had a required parameter after a non-required one (Closure Compiler dislikes this)
  • using same type annotation for _.uniq and _.unique, since the latter is an alias for the former
  • beginning to add type annotations for functional-style usage of underscore, vs. object notation (e.g. _(collection).map(function(){}) vs., function() {}). The existing externs file has only the latter.

I’ll probably also be adding externs for use with the SVG library Raphael at some point.