Javascript几种创建对象的方法

1.工厂方法

demo.js
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function createPerson(name, age) {
    var person = new Object();
    person.name = name;
    person.age = age;

    person.sayHi = function() {
        return "name: " + this.name + " age: " + this.age;
    };

    return person;
}

优点:创建相同实例只有一处代码。
缺点:不知道对象原型。

test.js
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var person1 = createPerson("zhang", 20);
var person2 = createPerson("li", 30);

console.log(person1.sayHi());
console.log(person2.sayHi());

console.log(person1 instanceof Person); //false
console.log(person2 instanceof Person); //false

2.构造函数

demo.js
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function Person(name, age) {
    this.name = name;
    this.age = age;

    this.sayHi = function() {
        return "name: " + this.name + " age:" + this.age;
    };
}

优点:可以知道实例原型。
缺点:方法不是同一个方法实例。

test.js
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var person1 = new Person("zhang", 20);
var person2 = new Person("li", 30);

console.log(person1.sayHi()); //name: zhang age:20
console.log(person2.sayHi()); //name: li age:30

console.log(person1 instanceof Person); //true
console.log(person2 instanceof Person); //true

console.log(person1.sayHi == person2.sayHi); //false

3.原型方法

demo.js
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function Person() {}

Person.prototype.name = "zhang";
Person.prototype.age = 20;
Person.prototype.sayHi = function() {
    return "name: " + this.name + " age: " + this.age;
};

优点:共享方法实例对象。
缺点:每个实例需要定义非方法属性。

test.js
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var person1 = new Person();
var person2 = new Person();

person2.name = "li";
person2.age = 30;

console.log(person1.sayHi()); //name: zhang age:20
console.log(person2.sayHi()); //name: li age:30

console.log(person1 instanceof Person); //true
console.log(person2 instanceof Person); //true

console.log(person1.sayHi == person2.sayHi); //true

4.构造函数和原型的组合方法

demo.js
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function Person(name, age) {
    this.name = name;
    this.age = age;
}

Person.prototype.sayHi = function() {
    return "name: " + this.name + " age: " + this.age;
};

优点:非方法属性在构造函数中定义,方法属性则在原型中定义。

总结:最后一种方法是比较好的创建对象的方式,综合了前面3种方式的优点。每个实例对象都有自己实例属性的一份副本,但同时共享着方法的引用,最大限度节省了内存。

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