一、姿式一函數
var person = new object(); person.name = 'jack' person.age = 18; person.sayName = function(){ console.log(this.name);
二、姿式二(簡單方便,推薦使用)this
var person = { name: 'jack', age: 18, sayName: function(){ console.log(this.name); } }
function Person(name, age){ this.name = name, this.age = age, this.sayName = function(){ console.log(this.name); } } var p1 = new Person('jack', 18); p1.sayName(); // jack
在每個實例對象中同時有一個constructor屬性,該屬性指向建立該實例的構造函數prototype
function Person(name, age){ this.name = name, this.age = age, this.sayName = function(){ console.log('i am ' + this.name); } }; var p1 = new Person('alex', 18); var p2 = new Person('jason', 17); console.log(p1.constructor === Person); // true console.log(p1.constructor === p2.constructor); //true
檢測對象類型,使用instanceof更加靠譜指針
console.log(p1 instanceof Person); //true console.log(p2 instanceof Person); //true
對於每個實例來講,sayName都是如出一轍的內容每一次生成一個實例,都必須爲重複的內容,多佔用一些內存,若是實例對象不少,會形成極大的內存浪費code
var fns = { sayName: function(){ console.log("i am" + this.name); } } function Person(name, age){ this.name = name, this.age = age, this.sayName = fns.sayName } var p1 = new Person('alex', 18); p1.sayName();
上述方法解決了內存浪費的問題,可是看起來不夠優雅,終極解決方法prototype對象
JavaScript 規定,每個構造函數都有一個 prototype 屬性,指向另外一個對象。ip
function F(){}; console.log(F.prototype) // Object
構造函數的 prototype 對象默認都有一個 constructor 屬性,指向 prototype 對象所在函數。內存
console.log(F.prototype.constructor === F) // => true
經過構造函數獲得的實例對象內部會包含一個指向構造函數的 prototype 對象的指針 proto。原型
var instance = new F() console.log(instance.__proto__ === F.prototype) // => true
這也就意味着,咱們能夠把全部對象實例須要共享的屬性和方法直接定義在 prototype 對象上。io
function Person(name, age){ this.name = name this.age = age } Person.prototype.type = 'human'; Person.prototype.sayName = function(){ console.log(this.name); } var p1 = new Person('alex', 18); var p2 = new Person('jack', 18); console.log(p1.sayName === p2.sayName); //true
"contructor"並不表示(對象)被(它)構造
p1.contructor只是經過默認的[[Prototype]]委託指向Person和「構造」毫無關係。Person.prototype的。contructor屬性只是Person函數聲明時的默認屬性
function Person(name, age){ this.name = name, this.age = age, this.sayName = function(){ console.log('i am ' + this.name); } }; function Test(){ this.name = 'test'; } Person.prototype = { constructor: Test } var p1 = new Person('alex', 18); console.log(p1.constructor === Person) // false console.log(Person.prototype.constructor.name) // Test
function Person(name, age){ this.name = name, this.age = age } Person.Prototype = { contructor: Person, // => 手動將 constructor 指向正確的構造函數 防止原型對象丟失 type: 'human', sayName: function(){ console.log("I am " + this.name); } }