Javascript Compare two arrays with different sizes and return the items that are not in second array

Question

I have two arrays:

var array1 = [a,b,c,d];
var array2 = [1,2,a,b];

I need to have a function that returns an array of the items not in the second Array.

var notInSecond = [c,d];

Does anyone know how to do this?

Thanks.

Answer 1

var notInSecond = array1.slice(0); // Creates a clone of array1
for (var i = 0, j; i < array2.length; i++) {
    j = notInSecond.indexOf(array2[i]);
    if (j > -1) notInSecond.splice(j, 1);
}

Keep in mind that indexOf for arrays isn't available for IE8 and lower and it must be emulated. I'm also assuming that array1 doesn't contain duplicates.