SOURCE

// 实现 call
Function.prototype.myCall = function (context = window, ...args) {
    const key = Symbol();
    // 避免原有属性被覆盖
    context[key] = this;
    // 通过隐式绑定的方式调用函数
    const result = context[key](...args);
    // 不改变原对象
    delete context[key];
    //返回函数调用的返回值
    return result;
};

// 实现 apply
Function.prototype.myApply = function (context = window, args = []) {
    const key = Symbol();
    // 避免原有属性被覆盖
    context[key] = this;
    // 通过隐式绑定的方式调用函数
    const result = context[key](...args);
    // 不改变原对象
    delete context[key];
    //返回函数调用的返回值
    return result;
};

// 实现 bind
Function.prototype.myBind = function (context = window, ...args) {
    const fn = this
    return function newFn(...newFnArgs) {
        if (this instanceof newFn) {
            return fn.apply(this, [...args, ...newFnArgs])
        }
        return fn.apply(context, [...args, ...newFnArgs])
    }
};

function Func(a) {
    this.a = a;

    this.logA = function (arg1, arg2, arg2) {
        console.log(this.a, arg1, arg2)
    }
}

const obj = {
    a: 1,
    logA(arg1, arg2) {
        console.log(this.a, arg1, arg2)
    },
    getA(arg1, arg2) {
        return this.a + arg1 + arg2;
    }
}

window.a = 2

const obj2 = {
    a: 3
}

// const newFunc = Func.myBind(this, 2);
// const func = new newFunc(3);
// func.logA(4)


// const newObj = obj.bind

Function.prototype.newCall = function (context = window, ...args) {
    const key = Symbol();
    context[key] = this;
    const result = context[key](...args)
    delete context[key];
    return result;
}

Function.prototype.newApply = function (context = window, args = []) {
    const key = Symbol();
    context[key] = this;
    const result = context[key](...args)
    delete context[key];
    return result;
}

Function.prototype.newBind = function (context = window, ...args) {
    const fn = this;
    function newFn(...newArgs) {
        if (context instanceof newFn) {
            context.apply(context, [...args, ...newArgs])
        } else {
            context.apply(fn, [...args, ...newArgs])
        }
    }
}