所有 JavaScript 对象都继承属性和方法 来自原型。
在上一章中,我们学习了如何使用对象构造函数:
function Person(first, last, age, eyecolor) {
this.firstName = first;
this.lastName = last;
this.age = age;
this.eyeColor = eyecolor;
}
const myFather = new Person("John", "Doe", 50, "blue");
const myMother = new Person("Sally", "Rally", 48, "green");
自己尝试一下 →
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Objects</h2>
<p>Using an object constructor:</p>
<p id="demo"></p>
<script>
function Person(first, last, age, eye) {
this.firstName = first;
this.lastName = last;
this.age = age;
this.eyeColor = eye;
}
const myFather = new Person("John", "Doe", 50, "blue");
const 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,您不能向现有对象构造函数添加新属性:
Person.nationality = "English";
自己尝试一下 →
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Objects</h2>
<p>You cannot add a new property to a constructor function.</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";
const myFather = new Person("John", "Doe", 50, "blue");
const myMother = new Person("Sally", "Rally", 48, "green");
document.getElementById("demo").innerHTML =
"The nationality of my father is " + myFather.nationality;
</script>
</body>
</html>
要将新属性添加到构造函数,必须将其添加到 构造函数:
function Person(first, last, age, eyecolor) {
this.firstName = first;
this.lastName = last;
this.age = age;
this.eyeColor = eyecolor;
this.nationality = "English";
}
自己尝试一下 →
<!DOCTYPE html>
<html>
<body>
<h1>JavaScript Objects</h1>
<p>Using an object constructor:</p>
<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";
}
const myFather = new Person("John", "Doe", 50, "blue");
const myMother = new Person("Sally", "Rally", 48, "green");
document.getElementById("demo").innerHTML =
"The nationality of my father is " + myFather.nationality + ". The nationality of my mother is " + myMother.nationality;
</script>
</body>
</html>
所有 JavaScript 对象都从原型继承属性和方法:
Date
对象继承自 Date.prototype
Array
对象继承自 Array.prototype
Person
对象继承自 Person.prototype
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
。
有时您想要向给定类型的所有现有对象添加新属性(或方法)。
有时您想向对象添加新属性(或方法) 构造函数。
JavaScript prototype
属性允许您向对象添加新属性 构造函数:
function Person(first, last, age, eyecolor) {
this.firstName = first;
this.lastName = last;
this.age = age;
this.eyeColor = eyecolor;
}
Person.prototype.nationality = "English";
自己尝试一下 →
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Objects</h2>
<p>The prototype property allows you to add new methods to objects constructors:</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.prototype.nationality = "English";
const myFather = new Person("John", "Doe", 50, "blue");
document.getElementById("demo").innerHTML =
"The nationality of my father is " + myFather.nationality;
</script>
</body>
</html>
JavaScript prototype
属性还允许您向对象添加新方法 构造函数:
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;
};
自己尝试一下 →
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Objects</h2>
<p id="demo"></p>
<script>
function Person(first, last, age, eye) {
this.firstName = first;
this.lastName = last;
this.age = age;
this.eyeColor = eye;
}
Person.prototype.name = function() {
return this.firstName + " " + this.lastName
};
const myFather = new Person("John", "Doe", 50, "blue");
document.getElementById("demo").innerHTML =
"My father is " + myFather.name();
</script>
</body>
</html>
仅修改您自己的原型。切勿修改原型 标准 JavaScript 对象。