求两个数组的差集

/**
 * Created by Administrator on 2017/1/4.
 */
var a = [1, 2, 3];
var b = [2, 3, 4, 5];

function cha(a, b) {
    var res = [];
    for (var i = 0, len = a.length; i < len; i++) {
        if (b.indexOf(a[i]) === -1) {
            res.push(a[i]);
        }
    }
    for (var j = 0, len = b.length; j < len; j++) {
        if (a.indexOf(b[j]) === -1) {
            res.push(b[j]);
        }
    }
    return res;
}

alert(cha(a, b));//1,4,5