call&apply&bind的js实现以及应用

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applyFunction.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 & applyMath.max.apply(null, [3,5,88,2])在这里，我们看到了一个有趣的现象，在Math.max中可以传入数组 call&apply两大作用：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)