I got this one from Scott, who ran into this problem with his amazing SoundManager library.

The puzzler

What’s wrong with this code:

soundManager.sounds = [];
soundManager.createSound = function(soundID) {
  this.sounds[soundID] = new Sound(...);
}

// (user's stuff):
soundManager.createSound('join');

Try to figure this one out on your own before continuing!!!

The problem

The problem isn’t with the scope of the createSound() function as many people first think, but rather with the associative array sounds and using the key ‘join’.

When you’re saying sounds[‘join’] = ‘foobar’, you’re effectively trying to modify the Array’s built-in join() method. And while not all browsers throw an exception (Firefox 3 doesn’t), it’s bad practice!

The solution

Simply define the sounds variable as sounds = new Object() or sounds = {} when the need for an associative array arises and you’ll be all set. The Array class in JavaScript is an object with extra methods and functionality (like: sort(), join(), etc). Don’t risk of conflicting with those names by using an Array in these situations.

Enjoy quizzing your potential hires during the next interview!