javascript数组去掉重复字符

    Array.prototype.del = function() {
        var a = {}, c = [], l = this.length;
        for (var i = 0; i < l; i++) {
            var b = this[i];
            var d = (typeof b) + b;
            if (a[d] === undefined) {
                c.push(b);
                a[d] = 1;
            }
        }
        return c;
    }
    alert([1, 1, 2, 3, 4, 5, 4, 3, 4, 4, 5, 5, 6, 7].del());