JavaScript – separate (split) array

I often have a list from the server that I need to split into 2 separate arrays. For example, all options that are enabled and all that are not. Here’s a little extension to handle that. Takes a single callback as an argument, with map-style params (value, index, array) – if that iterated callback returns truthy, it’ll be spliced out of the calling array and pushed into the returned array.

​Array.prototype.separate = ​function(callback){
	var sep = [];
	for(var i = 0; i < this.length; i++){
		if(callback(this[i], i, this)){
			sep.push(this[i]);
			this.splice(i, 1);
			i--;
		}        
	}
	return sep;
};

var letters = ["A", 1, "B", "C", 2, "D", 3, "E"];

var numbers = letters.separate(function(element){
    return !isNaN(element);
});

alert(letters + "\n" + numbers);

Non-polluting:

function separateArrays(array, callback){
	var sep = [];
	for(var i = 0; i < array.length; i++){
		if(callback(array[i], i, array)){
			sep.push(array[i]);
			array.splice(i, 1);
			i--;
		}        
	}
	return sep;
};