JavaScript prototype原型用法

JavaScript对象原型

所有JavaScript对象都从原型继承属性和方法。

1<!DOCTYPE html>
2<html>
3<meta charset="utf-8">
4<title>js</title>
5<body>
6
7<h2>JavaScript 对象</h2>
8
9<p id="demo"></p>
10
11<script>
12function Person(first, last, age, eye) {
13   this.firstName = first;
14   this.lastName = last; this.age = age; this.eyeColor = eye; } var myFather = new Person("John", "Doe", 50, "blue"); var myMother = new Person("Sally", "Rally", 48, "green"); document.getElementById("demo").innerHTML = "My father is " + myFather.age + ". My mother is " + myMother.age; </script> </body> </html>

我们还了解到，您无法向现有对象构造函数添加新属性：

1<!DOCTYPE html>
2<html>
3<meta charset="utf-8">
4<title>JavaScript对象</title>
5<body>
6
7<h2>JavaScript对象</h2>
8
9<p>您无法向构造函数添加新属性。</p>
10
11<p id="demo"></p>
12
13<script>
14function Person(first, last, age, eye) {
15   this.firstName = first;
16   this.lastName = last; this.age = age; this.eyeColor = eye; } Person.nationality = "English"; var myFather = new Person("John", "Doe", 50, "blue"); var myMother = new Person("Sally", "Rally", 48, "green"); document.getElementById("demo").innerHTML = "The nationality of my father is " + myFather.nationality; </script> </body> </html>

要向构造函数添加新属性，必须将其添加到构造函数：

1<!DOCTYPE html>
2<html>
3<meta charset="utf-8">
4<title>JavaScript对象</title>
5<body>
6
7<h2> JavaScript对象</h2>
8
9<p id="demo"></p>
10
11<script>
12function Person(first, last, age, eye) {
13   this.firstName = first;
14   this.lastName = last; this.age = age; this.eyeColor = eye; this.nationality = "English"; } var myFather = new Person("John", "Doe", 50, "blue"); var myMother = new Person("Sally", "Rally", 48, "green"); document.getElementById("demo").innerHTML = "我父亲的国籍是 " + myFather.nationality + ". 我母亲的国籍是： " + myMother.nationality; </script> </body> </html>

原型继承

所有JavaScript对象都从原型继承属性和方法：

Object.prototype位于原型继承链的顶部：Date对象，Array对象和Person对象继承自Object.prototype。

* Date 对象继承自 Date.prototype
* Array 对象继承自 Array.prototype
* Person 对象继承自 Person.prototype

# 向对象添加属性和方法

有时，您希望向给定类型的所有现有对象添加新属性（或方法）。有时您想要向对象构造函数添加新属性（或方法）。

使用**原型**属性

JavaScript prototype属性允许您向对象构造函数添加新属性：

1function Person(first, last, age, eyecolor) {
2  this.firstName = first;
3  this.lastName = last;
4  this.age = age;
5  this.eyeColor = eyecolor;
6}
7Person.prototype.nationality = "English";

JavaScript prototype属性还允许您向对象构造函数添加新方法：

1function Person(first, last, age, eyecolor) {
2   this.firstName = first;
3   this.lastName = last;
4   this.age = age;
5   this.eyeColor = eyecolor; } Person.prototype.name = function() { return this.firstName + " " + this.lastName; };

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