JavaScript prototype原型用法

来源：cnblogs　　作者：web小哥　　时间：2019/7/29 9:08:11　　对本文有异议

JavaScript对象原型

所有JavaScript对象都从原型继承属性和方法。

<!DOCTYPE html>
<html>
<meta charset="utf-8">
<title>js</title>
<body>
 
<h2>JavaScript 对象</h2>
 
<p id="demo"></p>
 
<script>
function Person(first, last, age, eye) {
   this.firstName = first;
   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：

<!DOCTYPE html>
<html>
<meta charset="utf-8">
<title>JavaScript对象</title>
<body>
 
<h2>JavaScript对象</h2>
 
<p>您无法向构造函数添加新属性。</p>
 
<p id="demo"></p>
 
<script>
function Person(first, last, age, eye) {
   this.firstName = first;
   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：

<!DOCTYPE html>
<html>
<meta charset="utf-8">
<title>JavaScript对象</title>
<body>
 
<h2> JavaScript对象</h2>
 
<p id="demo"></p>
 
<script>
function Person(first, last, age, eye) {
   this.firstName = first;
   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：

function Person(first, last, age, eyecolor) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eyecolor;
}
Person.prototype.nationality = "English";

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

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