Monday, January 31, 2011

Fixing javascript variable leaks

Today I happended to have a look at my application's window object and was shocked to see that 'i' was defined on it! I doggedly started searching my code to see where the leak had perpetrated itself from. After an hour of debugging, which included using Google's online closure compiler (Thanks Sandy!!) and jslint, I came up with nothing.

It struck me that it could be some of the js-libraries that I was using that were causing the leak, and not my code. I tried doing a binary-search on the js-includes, but that didn't work since the code wouldn't even run without most of those includes. At this point I really didn't know how to even go about trying to fix it!!

A few hacky thoughts later, I decided to introduce this code in my application:
var _iv = setInterval(function() {
  if (typeof window.i != "undefined") {
}, 10);

Of course, this relied on the fact that I had inserted a verbiage of console.log() statements in my code at various points (It actually helped to have them!!)

This bit of hackery at least helped me determine that the error happened after a certain set of statements (functions) had executed. From here, it was manual work, checking every function and callback (yes) in my code as well as any library that I was using.

After about 30 minutes, I was able to trace the leak to's jQuery library. I also discovered that the fb-complete jQuery library I was using had this leak, but it wasn't the one responsible for the specific instance of the variable 'i' that I was seeing then.

Sunday, January 30, 2011

When to use events & when to use callbacks?

With the recent spate of javascript programming that I've been subject to, I've found myself asking this question quite often to myself "Should I use callbacks here or should I use events (jQuery trigger & bind)?"

I've found this initial approximation quite useful till now: "If the operation that will follow depends upon the exact instance of this operation, then wrap the state in a closure and use a callback. Otherwise, use events." The advantage of using events is that:
1. You need not think of all the actions that could result in this event handler being called.
2. You need not tell anyone that this particular event handler needs to be invoked. Everyone just publishes some data (like a tweet) and all those interested (followers) just gobble that data up.
3. You can dynamically attach event handlers. So, if some component in the system suddenly decided to react to certain events, it can just plonk itself into to the listeners queue for that event.

jQuery goes one step further and allows you to trigger (and bind) events on specific DOM nodes only!! And then it goes a step further and lets you define an event namespace to try and prevent event name conflicts.