JavaScript Accessors (Getters and Setters) #
ECMAScript 5 (2009) introduced Getter and Setters.
Getters and setters allow you to define Object Accessors (Computed Properties).
JavaScript Getter (The get Keyword) #
This example uses a lang
property to get
the value of the language
property.
Example #
// Create an object:
var person = {
firstName: "John",
lastName : "Doe",
language : "en",
get lang() {
return this.language;
}
};
// Display data from the object using a getter:
document.getElementById("demo").innerHTML = person.lang;
var person = {
firstName: "John",
lastName : "Doe",
language : "",
set lang(lang) {
this.language = lang;
}
};
// Set an object property using a setter:
person.lang = "en";
// Display data from the object:
document.getElementById("demo").innerHTML = person.language;
var person = {
firstName: "John",
lastName : "Doe",
fullName : function() {
return this.firstName + " " + this.lastName;
}
};
// Display data from the object using a method:
document.getElementById("demo").innerHTML = person.fullName();
Example 2 #
var person = {
firstName: "John",
lastName : "Doe",
get fullName() {
return this.firstName + " " + this.lastName;
}
};
// Display data from the object using a getter:
document.getElementById("demo").innerHTML = person.fullName;
Example 1 access fullName as a function: person.fullName().
Example 2 access fullName as a property: person.fullName.
The second example provides simpler syntax.
Data Quality #
JavaScript can secure better data quality when using getters and setters.
Using the lang
property, in this example, returns the value of the language
property in upper case:
Example #
// Create an object:
var person = {
firstName: "John",
lastName : "Doe",
language : "en",
get lang() {
return this.language.toUpperCase();
}
};
// Display data from the object using a getter:
document.getElementById("demo").innerHTML = person.lang;
Using the lang
property, in this example, stores an upper case value in the language
property:
Example #
var person = {
firstName: "John",
lastName : "Doe",
language : "",
set lang(lang) {
this.language = lang.toUpperCase();
}
};
// Set an object property using a setter:
person.lang = "en";
// Display data from the object:
document.getElementById("demo").innerHTML = person.language;
Why Using Getters and Setters? #
- It gives simpler syntax
- It allows equal syntax for properties and methods
- It can secure better data quality
- It is useful for doing things behind-the-scenes
Object.defineProperty() #
The Object.defineProperty()
method can also be used to add Getters and Setters:
Example #
// Define object
var obj = {counter : 0};
// Define 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 Setters are not supported in Internet Explorer 8 or earlier:
Yes | 9.0 | Yes | Yes | Yes |