There is a very good post about Associative Arrays considered harmful by Andrew Dupont.

The title is a bit misleading but correct. When coming accross a piece of JavaScript like this
foo["test"] = 1;
there is nothing wrong about it. It's the basic usage scheme of assoziative arrays. Or should i rather say objects?

While in languages such as PHP arrays used like this $foo = array("test" => 1); is perfectly correct.

In JavaScript
var foo = new Array();
foo["test"] = 1;
works but does not do what you want.

I don't need to repeat Andrew's really great post, but basically you should use Object instead of Array.

var foo = new Object(); // same as var foo = {};
foo["test"] = 1; // same as foo.test = 1;

Now go and read Andrew's post.

via Erik Arvidsson.

btw: that post lead me to Object.prototype is verboten which explains for me why my for (i in myvar) {} loops never worked correctly. I was using prototype.js version < 1.4 (which messed with Object.prototype).

javascript, array, object, prototype.js, Object.prototype