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C # tutorial
ECMAScript 5 (ES5 2009) introduced Getter and Setters
ECMAScript 5 (ES5 2009) introduced Getter and Setters.
Getters and setters allow you to define Object Accessors (Computed Properties).
This example uses a lang
property to get
the value of the language
property.
// Create an object:
const 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;
This example uses a lang
property to set
the value of the language
property.
const 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;
What is the differences between these two examples?
const 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();
const 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 a simpler syntax.
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:
// Create an object:
const 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:
const 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;
The Object.defineProperty()
method can also be used to add Getters and
Setters:
// Define object
const obj = {counter : 0};
// Define setters and getters
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;