手写Array.prototype.pop

前端知识复习 code snippet

array.prototype.pop 标准

1. Let O be ? ToObject(this value).
2. Let len be ? LengthOfArrayLike(O).

3. If len is zero, then

   • Perform ? Set(O, "length", 0, true).
   • Return undefined.

4. Else,

   • Assert: len > 0.
   • Let newLen be len - 1.
   • Let index be ! ToString(newLen).
   • Let element be ? Get(O, index).
   • Perform ? DeletePropertyOrThrow(O, index).
   • Perform ? Set(O, "length", newLen, true).
   • Return element.

代码

Array.prototype.myPop = function () {
    var O = Object(this);
    var len = O.length >>> 0;

    if (len == 0) {
        O.length = 0;
        return undefined;
    } else {
        var element = O[--len];
        delete O[len];
        O.length = newLen;
        return element;
    }
};