函数方法

new 构造函数

参考：https://juejin.cn/post/6844903937405878280

function myNew(Obj, ...args) {
    const obj = Object.create(Obj.prototype);
    const res = Obj.apply(obj, args);
    return typeof res === 'object' ? res : obj;
}

构造函数如果存在返回值（return）：

1. 返回值为对象：则new出来的值就是返回的对象
2. 返回值为非对象：没有影响

call

Function.prototype.myCall = function (context, ...args) {
    context = typeof context === 'object' ? context : window;

    const key = Symbol();
    context[key] = this;
    const res = context[key](...args);
    Reflect.deleteProperty(context, key);

    return res;
};

apply

Function.prototype.myApply = function (context, args) {
    context = typeof context === 'object' ? context : window;
    if (!Array.isArray(args)) {
        throw new TypeError('args must be an array.');
    }

    const key = Symbol();
    context[key] = this;
    const res = context[key](...args);
    Reflect.deleteProperty(context, key);

    return res;
};

bind

Function.prototype.myBind = function (context, ...innerArgs) {
    context = typeof context === 'object' ? context : window;
    return (...outerArgs) => this.call(context, ...innerArgs, ...outerArgs);
};