原生JS数组方法实现(一）————push()、unshift()、pop()和shift()

function push(){
   for(let i=0;i<arguments.length;i++){
       this[this.length] = arguments[i];
   }
    return this.length
}
Array.prototype.push = push;

function unshift(){
    //创建一个新数组接收添加的元素
    let newAry = [];
    for(let i=0;i<arguments.length;i++){
        newAry[i] = arguments[i];
    }
    let len = newAry.length;
    for(let i=0;i<this.length;i++){
        newAry[i+len] = this[i];
    }
    for(let i=0;i<newAry.length;i++){
        this[i] = newAry[i];
    }
    return this.length;
}
Array.prototype.unshift = unshift;

function pop(){
    let returnVal = this[this.length-1];
    this.length--;
    return returnVal
}
Array.prototype.pop = pop;

function shift(){
    let newAry = [];
    let reVal = this[0];
    for(let i=0;i<this.length-1;i++){
        newAry[i] = this[i+1];
    }
    for(let i=0;i<newAry.length;i++){
        this[i] = newAry[i]
    }
    this.length--;
    return reVal;
}
Array.prototype.shift = shift;