Javascript 练习

在Array()构造器以及相关的数组文本标识法都不存在的情况下，自定义一个类似的MyArray()构造器，并令其通过以下测试：

var a = new MyArray(1,2,3,"test");
a.toString();
//"1,2,3,test"

a.length;
//4

a[a.length-1];
//"test"

a.push("boo");
//5

a.toString();
//"1,2,3,test,boo"

a.pop();
//boo

a.toString();
//"1,2,3,test"

a.join(",");
//"1,2,3,test"

a.join(" isn\'t");
//1 isn't 2 isn't 3 isn't test"

function MyArray() {
    this.length = arguments.length;

    for (var i=0; i<this.length; i++){
        this[i] = arguments[i];
    }

    this.toString = function () {
        var string = "";
        for (var i=0; i<this.length; i++){
            string += string ? (", "+this[i]) : this[i];
        }
        return string;
    };

    this.push = function (elem) {
        this[this.length] = elem;
        this.length++;
    };

    this.pop = function () {
        return this[--this.length];
    };

    this.join = function (sep) {
        var string = "";
        for(var i=0; i<this.length; i++){
            string += this[i] + ((i==this.length-1) ? "": sep);
        }
        return string;
    };
}

var a = new MyArray(1, 2, 3, "test");

console.log(a.toString());
console.log(a.length);
console.log(a[a.length-1]);
a.push("boo");
console.log(a.toString());
a.pop();
console.log(a.toString());
console.log(a.join(","));
console.log(a.join(" isn\'t "));