二つのグループを比較して、違った内容を探し出す.

//     ，a,b
var a = ["qwe","asd"];
var b = ["zxc","qwe"];

//         
Array.prototype.minus = function (arr) {
        var result = new Array();
        var obj = {};
        for (var i = 0; i < arr.length; i++) {
            obj[arr[i]] = 1;
        }
        for (var j = 0; j < this.length; j++) {
            if (!obj[this[j]]) {
                obj[this[j]] = 1;
                result.push(this[j]);
            }
        }
        return result;
    };

//     a     
console.log(a.minus(b));
//     b     
console.log(b.minus(a));