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JavaScript prototype原型用法

程序员文章站 2022-03-23 13:39:19
JavaScript prototype原型用法,所有JavaScript对象都从原型继承属性和方法。 ......

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;
};

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