18.类数组

属性要为索引(数字)属性,必须有length属性,最好加上push

var obj = {

    "0" : 0,

    "1" : 1,

    "length":2,

    "push":Array.prototype.push,    

    "splice":Array.prototype.splice

}

obj.push("c");

obj.push("d")

Array.prototype.push = function(target){

        obj[obj.length] = target;

        obj.length ++;

}