实现数组的原型方法

pop 方法

var arr=[1,7,4,9,3];
Array.prototype.ppop = function () {
    var arr = this;
    arr.length--;
    return arr;
};
console.log(arr.ppop());

---

push 方法

var arr = [1, 7, 4, 9, 3];

Array.prototype.ppush = function (value) {
    this[this.length] = value;
    return this;
};
console.log(arr.ppush(2));

---

slice 方法

var arr = [1, 7, 4, 9, 3];

Array.prototype.sslice = function () {
    
    var star = arguments[0] < 0 ? this.length + arguments[0] : arguments[0];
    var end = arguments[1] < 0 ? this.length + arguments[1] : arguments[1];
    var newArray = [];
    newArray.length = end - star;
    for (var i = star, j = 0; i < end; i++, j++) {
        newArray[j] = this[i];
    }
    return newArray;
};
console.log(arr.sslice(-3, -1));

---

splice方法

备注：这个实现比起 pop ，push 略有复杂，应该是数组方法中最难的方法了。

var arr = [1, 7, 4, 9, 3];

Array.prototype.ssplice = function () {

    var dele = [];
    dele.length = arguments[1];
    var arr = this;
    //删除指定元素
    for (var i = 0, key = arguments[0]; i < arguments[1]; i++, key++) {
        dele[i] = arr[key];
        arr[key] = arr[key + arguments[1]];
    }
    arr.length -= arguments[1];

    var addCount = arguments.length - 2;

    //移动位置为添加的元素预留位置
    arr.length += addCount;
    for (var move = arr.length - 1; move > arr.length - addCount - arguments[0]; move--) {
        arr[move] = arr[move - addCount];
    }

    //添加新元素
    for (var addArr = arguments[0], newNumber = 2; addArr < addCount + arguments[0]; addArr++, newNumber++) {
        arr[addArr] = arguments[newNumber];
    }

    return dele;
};

console.log(arr.ssplice(2, 2, 6, 4));
console.log(arr);