How to remove all undefined keys from a javascript array (hopefully when creating the array?)

I have placed my frustrations into a jsfiddle to observe here: http://jsfiddle.net/8ShFr/1/ ``` var brand_new_array = new Array(); brand_new_array[10] = "random array value"; alert('why does this array have a length of ' + brand_new_array.length + '???'); ``` I am doing some calculations client side that require me to set javascript array keys of 1M+ in number. Not knowing exactly what that number is demands that I iterate through the first 1M+ empty array values before getting to an array key that holds data. I simply want to set a single large key value for a javascript array without creating a bunch of empty keys before it? I am using jQuery.each to iterate over the array, and it keeps going through `array[0]`, `array[1]`, `array[2]`, etc... when I only set `array[123125]` for example.