js实现call

// examplelet obj = {    a: 124,    b: 'ccc'};function fn(c) {    return this.a + this.b + this.c;}// 使用call是这样转换的// step 1: 生成新的函数，新的执行上下文(通过在传入对象中增加调用方法)const obj = {    a: 124,    b: 'ccc',    fn: function(c) {        return this.a + this.b + this.c;    }}// step2: 执行 obj.fn(333);let res = obj.fn(333);// step3: obj被改变，得恢复原来的值delete obj.fn;

Function.prototype.myCall = function(context) {    const newContext = context || window;    newContext.fn = this;    const args = [];    for(let i = 1; i < arguments.length; i++) {        args.push(arguments[i]);    }    const res = newContext.fn(...args);    delete newContext.fn;    return res;}console.log(fn.myCall(obj, 'cccc'));

js实现apply

Function.prototype.myApply = function(context, arr) {    const newContext = context || window;    newContext.fn = this;    const args = [];    let res;    if (!arr) {        res = newContext.fn(...args);    }    else {        if (!(arr instanceof Array)) {            throw new Error('params must be array');        }        result = context.fn(...arr);    }    delete newContext.fn;    return res;    }console.log(fn.myApply(obj, ['cccc']));

call & apply

Math.max.apply(null, [3,5,88,2])

改变this

借用其他对象的方法

改变this

如何实现Function.prototype.bind()

Function.prototype.bind = function(){    var self = this,        context = [].shift.apply(arguments);        args = [].slice.apply(arguments);        return function(){        return self.apply(context, [].concat.apply(args, [].slice.apply(arguments)))    };}//执行var obj = {    name: 'yyh'}var func = function(a, b, c, d){    console.log(this.name);}.bind(obj, 1, 2);func(3, 4);

借用其他对象的方法

继承的实现

var aFn = function(){    this.name = 'yyh'}var bFn = function(){    aFn.apply(this, arguments);}bFn.prototype.getName = function(){    return this.name}//执行var b = new bFn();console.log(b.getName())

能借用数组的方法，Obj.array.push, 需要满足两个条件

• Obj的属性可存取
• length属性可读写

var a = {c:3};[].push.apply(a, [3,4,5])console.log(a)