Is there a reason JavaScript developers don't use Array.push()?

I commonly see developers use an expression like the following in JavaScript:

arr = []
arr[arr.length] = "Something"
arr[arr.length] = "Another thing"

Wouldn't push be more appropriate?

arr = []
arr.push("Something")
arr.push("Another thing")

I actually asked myself the same question at the start of this year. UPDATED with new test cases http://jsperf.com/array-push-vs-unshift-vs-direct-assignment/2

It appears that push is much faster in chrome, and about equal in FF. Also direct is faster in IE9, but I would be interested to see how it performs in IE10.

I would say that most developers would assume setting the length of the array, and then using direct assignment is faster, as is the case with most programming languages. But JavaScript is different. Javascript arrays aren't really arrays, they're just key/value maps just like all other JavaScript objects. So the pre-allocation is essentially falling on deaf ears.

Personally I prefer push (:

I believe that it's mostly habit.

Some developers use it simply because it's the way they are used to do it, and haven't considered that push would be an alternative.

Some developers have learned once upon a time that one method is much faster than another, and haven't reviewed this in light of the recent performance improvements of the Javascript engines.

Personally I use push frequently. Most of the time readability and maintainability is more important than performance, at least when the performance impact is small enough. The performance tests posted in the answers here show that the performance difference between various methods isn't very big.