js简单算法（二）如何去除一个数组中与另一个数组中的值相同的元素

codewars上面6kyu的算法题，下面是算法题的英文简介

Your goal in this kata is to implement an difference function, which subtracts one list from another.

It should remove all values from list a, which are present in listb.

difference([1,2],[1]) == [2]

If a value is present in b, all of its occurrences must be removed from the other:

difference([1,2,2,2,3],[2]) == [1,3]

以下是我的解答，可以作为参考

function array_diff(a, b) {
    for(var i=0;i