js如何安全扩展系统函数

Array.prototype.first=function(){};

var ArrayEx = (function(){
  function ArrayEx(array){
    this.array = array || [];
  }
  ArrayEx.prototype.first= function (filter, context) {//获取首个数组元素
    filter = filter || function () { return true; };
    for (var i = 0, len = this.array.length; i < len; i++) {
        if (filter.call(context, i, this.array[i])) {
            return this.array[i];
        }
    }
    return null;
};

return ArrayEx;
}());

var node = new ArrayEx([1,2,3]).first(function(i,item){
  return item===3;
});
alert(node);