手写call，apply，bind

为了更好的理解call，apply，bind，研究了一下怎么手写这些方法

1.手写call

    Function.prototype.Call = function (content = window) {
        content.fn = this; //this指向调用它的对象  即bar方法
        let args = [...arguments].slice(1);//取得参数列表
        let result = content.fn(...args);
        return result;
    };
    let person = {
        name: '张三'
    };

    function fn(sex, age) {
        console.log(this.name + sex + age);
    }

    fn.Call(person, '男', '18岁') // 张三男18岁

2.手写apply

    Function.prototype.Apply = function (content = window) {
        content.fn = this;
        let result;
        // 判断是否有第二个参数
        if(arguments[1]) {
            result = content.fn(...arguments[1])
        } else {
            result = content.fn()
        }
        return result
    };

3.手写apply

    Function.prototype.Bind = function (content) {
        if (typeof this != 'function') {
            throw Error('not a function')
        }
        // 若没问参数类型则从这开始写
        let fn = this;
        let args = [...arguments].slice(1);
        console.log(arguments);
        console.log(...arguments);
        let resFn = function () {
            return fn.apply(this instanceof resFn ? this : content, args.concat(...arguments))
        };
        return resFn;
    };


    this.value = 2;
    let foo = {
        value: 1
    };
    let bar = function(name, age, school) {
        console.log(name); // 'An'
        console.log(age); // 22
        console.log(school) // '家里蹲大学'
    };
    let result = bar.Bind(foo, 'An'); //预置了部分参数'An'
    result(22, '家里蹲大学') //这个参数会和预置的参数合并到一起放入bar中