[TOC] # 1.原型鏈 JavaScript 規定，所有對象都有自己的原型對象（prototype）。一方面，任何一個對象，都可以充當其他對象的原型 > 所有對象皆有__proto__屬性,它指向它的原型對象 # 2.繼承 如何改變this關鍵字的指向call,apply,bind ## 2.1.函數作為普通函數調用,this指向window ``` function show(){ console.log(this); } show(); //window ``` ``` var name = "cheng" function show(){ console.log(this.name); } show(); ``` ## Call ``` var name = "cheng" function show(){ console.log(this.name); } var zhang = { name:"張三" } show.call(zhang); ``` ## Apply ``` var name = "cheng" function show(){ console.log(this.name); } var zhang = { name:"張三" } show.apply(zhang); ``` ## Call和apply之間的區別 如果要傳遞參數,apply跟數組 eg: ``` function show(a,b){ console.log(this.name); console.log(a+b) } var zhang = { name:"張三" } //show.call(zhang,1,2) show.apply(zhang,[1,2]); ``` ## Bind bind后函數不會執行，而只是返回一個改變了上下文的函數副本，而call和apply是直接執行函數 **demo01** ``` <div id="text">div</div> <button id="btn">btn</button> var id = "world" var btn = document.getElementById("btn"); var text = document.getElementById("text"); btn.onclick = function(){ console.log(this.id); //world }.bind(this); ``` **demo02** ``` var name = "li"; var cheng = { name:"cheng" } var test = function(){ console.log(this.name) }.bind(cheng); test(); ``` **demo03定時器** Eg：在函數內部的定時器中 ``` <div id="text">div</div> <button id="btn">btn</button> <script> var id = "world" var btn = document.getElementById("btn"); var text = document.getElementById("text"); btn.onclick = function(){ setTimeout(function(){ console.log(this.id); //world },1000) } </script> ``` ### 解決方案01 bind ``` <div id="text">div</div> <button id="btn">btn</button> <script> var id = "world" var btn = document.getElementById("btn"); var text = document.getElementById("text"); btn.onclick = function(){ setTimeout(function(){ console.log(this.id); }.bind(this),1000) } </script> ``` ### 解決方案 02 self ``` var id = "world" var btn = document.getElementById("btn"); var text = document.getElementById("text"); btn.onclick = function(){ var self = this; setTimeout(function(){ console.log(self.id); },1000) } ``` ### 解決方案 03 箭頭函數 ``` <button id="btn">btn</button> <script> var id = "world" var btn = document.getElementById("btn"); var text = document.getElementById("text"); btn.onclick = function(){ setTimeout(()=>{ console.log(this.id) },1000) } </script> ``` # 3.繼承實現 ``` var Person = function(name,age){ this.name = name; this.age = age; } Person.prototype.see = function(){ console.log(this.name+"愛看片") } function Teacher(name,age){ Person.call(this,name,age); } Teacher.prototype = new Person(); var cheng = new Teacher("cheng",20); cheng.see(); ```