Preallocation

Instead of declaring a new Array and reserving memory for it, you can reallocate an Array previously declared.

For that, you need to remove the previous contents of the array. You can do that setting Array.prototype.length to 0:

var array = [1, 2, 3, 4, 5]

array = [] //  bad
array.length = 0 // good!

Another good tip is to reserve the necessary memory space for your Array by setting its .length beforehand.

var array = []
arr.length = 5

arr[0] = 1
arr[1] = 2
arr[2] = 3

That useful when you want to use an Array as temporal data buffer. array-list is a good library for that.