摘要：面向?qū)ο笾饕R(shí)點(diǎn)小結(jié)，基于構(gòu)造函數(shù)可以理解為通過即將創(chuàng)建的對(duì)象將類實(shí)例化給一個(gè)對(duì)象賦予屬性或者方法原型便于方法的重用與構(gòu)造函數(shù)模式相比，使用原型對(duì)象的好處是可以讓所有對(duì)象實(shí)例共享它所包含的屬性和方法。

JavaScript面向?qū)ο笾饕R(shí)點(diǎn)小結(jié)，基于ECMAScript 5.

function People(name){
    //this可以理解為通過new即將創(chuàng)建的對(duì)象
    this.name = name;
}
//將類實(shí)例化
var person = new People("Cassie Xu");
console.log(person.name);

給一個(gè)對(duì)象賦予屬性或者方法

function People(name) {
  this.name = name;
  this.greet = function() {
    console.log("Hello, my name is " + this.name + "!");
  };
}
var person = new People("Cassie Xu");
person.greet();

why we use prototype? -> 便于方法的重用
與構(gòu)造函數(shù)模式相比，使用原型對(duì)象的好處是可以讓所有對(duì)象實(shí)例共享它所包含的屬性和方法。
運(yùn)行時(shí)沒找到函數(shù)的方法時(shí)，對(duì)象會(huì)首先找它的類的prototype方法
Demo1

function People(name) {
  this.name = name;
}
People.prototype = {
  greet: function() {
    console.log("Hello, my name is " + this.name + "!");
  }
};
var person = new People("Cassie Xu");
person.greet();
//在每個(gè)實(shí)例化后的對(duì)象都會(huì)有一個(gè)__proto__屬性,類會(huì)將它的prototype賦給實(shí)例
//實(shí)例化一個(gè)對(duì)象時(shí)，People這個(gè)類首先會(huì)將person的__proto屬性指向People.prototype
console.log(person.__proto__ === People.prototype); // true

Demo2

var a = { foo: 1 };
var b = { bar: 2 };
b.__proto__ = a;
//b本身沒有foo屬性，但是b會(huì)繼續(xù)尋找__proto__屬性
console.log(b.foo); // 1
console.log(b.bar); // 2

var a = {};
console.log(a.__proto__); // {}
console.log(a.__proto__.__proto__); // null

var a = {};
console.log(a.__proto__); // {}
console.log(a.__proto__.__proto__); // null

Demo1

function Parent(){}
Parent.prototype = {
    greet: function(){
    console.log("hello world");
}
}
function Child(){}
//此方法適用于父類Child不需要傳參數(shù)
Child.prototype = new Parent();
var c = new Child();
//c首先尋找自身的方法，沒有g(shù)reat,所以找Child的原型方法，而Child.prototype等于Parent方法
c.greet(); //console.log("hello world");

上面的例子如果Parent有參數(shù)，將存在以下問題：

function Parent(a, b) {}
Parent.prototype.greet = function() {
  console.log("JavaScript rocks");
}
function Child(a, b) {}
Child.prototype = new Parent(); //something wrong?->new Parent()不能傳參數(shù)，否則參數(shù)一直不變
var child = new Child();
child.greet();

Demo2
解決父類參數(shù)問題

function Parent() {
    this.name = "xxx",
    this.date = "xxx"
}
Parent.prototype.greet = function() {
  console.log("JavaScript rocks");
}
function Child() {}
//此方法適用于
Child.prototype = Object.create(Parent.prototype);
//硬記的知識(shí) 
Child.prototype.constructor = Child;
var child = new Child();
child.greet();

Demo3:繼承的一個(gè)實(shí)例
創(chuàng)建一個(gè)矩形

function Rect(width,height){
    this._setupDOM(width,height);
}
Rect.prototype._setupDOM = function(width,height){
    this._dom = document.createElement("div");
    this._dom.style.width = width + "px";
    this._dom.style.height = height + "px";
};
Rect.prototype.appendToBody = function(){
    document.body.appendChild(this._dom);
};
function BlueRect(width,height){
  BlueRect._super.apply(this,arguments);
}
BlueRect.prototype = Object.create(Rect.prototype);
BlueRect.prototype.constructor = BlueRect;
BlueRect._super = Rect;
BlueRect.prototype._setupDOM = function(width,height){
  BlueRect._super.prototype._setupDOM.apply(this,arguments);
  this._dom.style.backgroundColor = "blue";
};
var br = new BlueRect(200,300);
br.appendToBody();

Demo:

function Rect(width,height){
    //私有屬性加_
    this._dom = document.createElement("div");
    this._dom.style.width = width + "px";
    this._dom.style.height = height + "px";
    this._dom.style.backgroundColor = "red";
}
Rect.prototype.appendToBody = function(){
    document.body.appendChild(this._dom);
};
var rect = new Rect(100,100);
rect.appendToBody();

修改上面demo:

function Rect(width,height){
    this._setupDom(width,height);
}
Rect.prototype._setupDom = function(width,height){
    //私有屬性加_
    this._dom = document.createElement("div");
    this._dom.style.width = width + "px";
    this._dom.style.height = height + "px";
    this._dom.style.backgroundColor = "red";
};
Rect.prototype.appendToBody = function(){
    document.body.appendChild(this._dom);
};
var rect = new Rect(100,100);
rect.appendToBody();

var person = {
    firstName: "Penelope",
    lastName: "Barrymore",
    sayFullName: function () {
        console.log(this.firstName + " " + this.lastName); //=> "Penelope Barrymore"
        console.log(person.firstName + " " + person.lastName); //=> "Penelope Barrymore"
    }
};
person.sayFullName();

嚴(yán)格模式下的this

funtion foo(){
    "use strict";
    console.log(this) //undefined
}

function foo(a, b) {
  console.log(this);
  console.log(a + b);
}
var fooBinding = foo.bind({ name: "Cassie Xu" });
fooBinding(1, 2);

上面code將輸出

[object Object] {
  name: "Cassie Xu"
}

call/apply方法都為調(diào)用Object方法，區(qū)別是apply將所有參數(shù)放到一個(gè)數(shù)組中去

function foo(a, b) {
  console.log(this);
  console.log(a + b);
}
foo.call({name:"Cassie Xu"}, 1, 2);
foo.apply({name:"Cassie Xu"}, [1, 2]);

why we use it? ->避免泄露全局變量

(function(c){
    var a = 1;
    var b = 2;
    console.log(a+b+c);
})(3)
// c = 3

var a = {};
a.foo = function(callback) {
  // do something and call callback in whatever way
}
a.bar = function() {
  this.num = 1;
  var that = this;
  //閉包，這里that可以訪問到a.bar的作用域
  this.foo(function(newNum) {
    that.num = newNum;
  });
  console.log(this.num);
}
a.bar();

本文轉(zhuǎn)自 JavaScript面向?qū)ο笾R(shí)點(diǎn)小結(jié)