javascript判断数组内是否重复的方法

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;}