自定义MyArray()

在Array()构造器不存在的情况下，自定义一个MyArray()构造器

function MyArray(arg){
    /*
        思路：
        当arg只有一个且是数字时:
            数组为arg的值对应个数的undefined
        当arg是多个参数时:
            形成一个数组
    */
    if(typeof arg==='number'&&arguments[1]===undefined){
        this.length=arg;
        return this;
    }

    //多个参数
    this.length=arguments.length;
    for (var i = 0; i < arguments.length; i++) {
        this[i]=arguments[i]
    };
    return this;
}

MyArray.prototype={
    constructor: MyArray,
    toString: function toString(){
        return this.join();
    },
    push: function push(){
        for (var i = 0; i < arguments.length; i++) {
            this[this.length+i]=arguments[i];
        };
        this.length+=arguments.length;
        return this.length;
    },
    pop: function pop(){
        var temp=this[this.length-1];
        delete this[this.length-1];
        this.length--;
        return temp;
    },
    join: function join(glue){
        var result='';
        if(glue===undefined){
            glue=',';
        }
        for(var i=0;i<this.length-1;i++){
            result+=this[i]===undefined?'':this[i];
            result+=glue;
        }
        //最后一个元素不加符号，所以写出来
        result+=this[i]===undefined?'':this[i];
        return result;
    }
}

测试

var a=new MyArray(5); a
MyArray {length: 5}length: 5__proto__: Object
a.join()
",,,,"
a=new MyArray(1,2,3,4,5);
MyArray {0: 1, 1: 2, 2: 3, 3: 4, 4: 5, length: 5}
a.join()
"1,2,3,4,5"
a.join(' isn\t')
"1 isn  2 isn   3 isn   4 isn   5"
a.toString
toString(){
        return this.join();
    }
a.toString()
"1,2,3,4,5"
a.push('heiha');
6
a
MyArray {0: 1, 1: 2, 2: 3, 3: 4, 4: 5, 5: "heiha", length: 6}
a.pop()
"heiha"