indexOf

var arr = [1,2,3];

    Array.prototype.indexOf = Array.prototype.indexOf || function(obj){
        for(var i = 0, len = this.length; i < len; i++){
            if(this[i] == obj){
                console.log("xx")
                return i;
            }
        }
    };

    console.log(arr.indexOf(3))

    

    //var str = "kengdie";
    //alert(str.indexOf("e"));// 测试 String.prototype.indexOf 没有兼容问题