老师，帮批改下吧

es6方式：
	class Myarray {
	    constructor(arr) {
	        this.arr = arr;
	    }
	    myPop() {
	        if (this.arr.length === 0) return undefined;
	        return Number(this.arr.splice(this.arr.length - 1, 1))
	    }
	    myPush() {
	        let _this = this;
	        Array.from(arguments, el => _this.arr.splice(_this.arr.length, 0, el))
	        return this.arr.length;
	    }
	}
	let arr = Array.of(1, 5, 6, 7, 8)
	let myArray = new Myarray(arr);
	console.log(myArray.myPop(), arr)
	console.log(myArray.myPush(null), arr)

直接挂载方式
	Array.prototype.myPop = function () {
	    if (this.length === 0) return undefined;
	    return Number(this.splice(this.length - 1, 1))
	}
	Array.prototype.myPush = function () {
        let _this = this;
        Array.from(arguments, el => _this.splice(_this.length, 0, el))
        return _this.length;
	}
	 console.log(arr.myPop(), arr)
	 console.log(arr.myPush(0, 3, 4, 3, 2), arr)