Learn more about JavaScript object accessors (Getter and Setter)
Nov 29, 2019 pm 02:39 PM
JavaScript Accessors (Getters and Setters), ECMAScript 5 (2009) introduced Getters and Setters. Getters and setters allow you to define object accessors (Computed Properties).
[Related course recommendations: JavaScript video tutorial]
JavaScript Getter (get keyword)
<!DOCTYPE html>
<html>
<meta charset="utf-8">
<title>js</title>
<body>
<h2>JavaScript Getters和Setters</h2>
<p> Getters和setter允許您通過方法獲取和設置屬性。</p>
<p>此示例使用lang屬性獲取語言屬性的值。</p>
<p id="demo"></p>
<script>
// 新建一個對象。
var person = {
firstName: "John",
lastName : "Doe",
language : "en",
get lang() {
return this.language;
}
};
// 使用getter顯示來自對象的數(shù)據(jù)：
document.getElementById("demo").innerHTML = person.lang;
</script>
</body>
</html>JavaScript Setter (set keyword)
<!DOCTYPE html>
<html>
<meta charset="utf-8">
<title>JavaScript Getters和Setters</title>
<body>
<h2> JavaScript Getters和Setters </h2>
<p> Getters和setter允許您通過方法獲取和設置屬性。</p>
<p>此示例使用lang屬性設置語言屬性的值。</p>
<p id="demo"></p>
<script>
// Create an object:
var person = {
firstName: "John",
lastName : "Doe",
language : "NO",
set lang(value) {
this.language = value;
}
};
// Set a property using set:
person.lang = "en";
// Display data from the object:
document.getElementById("demo").innerHTML = person.language;
</script>
</body>
</html>Use JavaScript function or Getter?
What is the difference between these two examples?
Example 1:
var person = {
firstName: "John",
lastName : "Doe",
fullName : function() {
return this.firstName + " " + this.lastName;
}
};
// 使用方法顯示對象的數(shù)據(jù)：
document.getElementById("demo").innerHTML = person.fullName();Example 2:
var person = {
firstName: "John",
lastName : "Doe",
get fullName() {
return this.firstName + " " + this.lastName;
}
};
// 使用getter顯示來自對象的數(shù)據(jù)：
document.getElementById("demo").innerHTML = person.fullName;Example 1 Access fullName as a function: person.fullName(). Example 2 accesses fullName as a property: person.fullName. The second example provides simpler syntax.
Data Quality
JavaScript ensures better data quality when using getters and setters. lang In this example, the attribute language is used to return the value of the attribute in uppercase:
// 創(chuàng)建一個對象:
var person = {
firstName: "John",
lastName : "Doe",
language : "en",
get lang() {
return this.language.toUpperCase();
}
};
// 使用getter顯示來自對象的數(shù)據(jù)：
document.getElementById("demo").innerHTML = person.lang;lang In this example, the attribute language is used to store the uppercase value in the language attribute:
var person = {
firstName: "John",
lastName : "Doe",
language : "",
set lang(lang) {
this.language = lang.toUpperCase();
}
};
// 使用setter設置對象屬性：
person.lang = "en";
// 顯示來自對象的數(shù)據(jù)：
document.getElementById("demo").innerHTML = person.language;Why use Getter and Setter?
● It provides a simpler syntax
● It allows the same syntax for properties and methods
● It ensures better data quality
●It’s useful to do things behind the scenes
<!DOCTYPE html>
<html>
<meta charset="utf-8">
<title>js</title>
<body>
<h2> JavaScript Getters和Setters </h2>
<p>完美的創(chuàng)建反對象：</p>
<p id="demo"></p>
<script>
var obj = {
counter : 0,
get reset() {
this.counter = 0;
},
get increment() {
this.counter++;
},
get decrement() {
this.counter--;
},
set add(value) {
this.counter += value;
},
set subtract(value) {
this.counter -= value;
}
};
// Play with the counter:
obj.reset;
obj.add = 5;
obj.subtract = 1;
obj.increment;
obj.decrement;
// Display the counter:
document.getElementById("demo").innerHTML = obj.counter;
</script>
</body>
</html>Object.defineProperty()
The Object.defineProperty() method can also be used to add Getters and Setter:
// 定義對象
var obj = {counter : 0};
// 定義 setters
Object.defineProperty(obj, "reset", {
get : function () {this.counter = 0;}
});
Object.defineProperty(obj, "increment", {
get : function () {this.counter++;}
});
Object.defineProperty(obj, "decrement", {
get : function () {this.counter--;}
});
Object.defineProperty(obj, "add", {
set : function (value) {this.counter += value;}
});
Object.defineProperty(obj, "subtract", {
set : function (value) {this.counter -= value;}
});
// Play with the counter:
obj.reset;
obj.add = 5;
obj.subtract = 1;
obj.increment;
obj.decrement;Browser support
Getters and Setter are not supported in Internet Explorer 8 or earlier:
| Internet Explorer | Chrome | FireFox | Safari | Opera |
|---|---|---|---|---|
 |
 |
 |
 |
 |
| Support | Support | Support | Support |
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