JavaScript Object Accessors

JavaScript Getters 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:
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;

Try it Yourself »

JavaScript Setter (The set Keyword)

This example uses a lang property to set the value of the language property.

Example

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;

Try it Yourself »

JavaScript Function or Getter?

What is the differences between these two examples?

Example 1

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();

Try it Yourself »

Example 2

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;

Try it Yourself »

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.

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:
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;

Try it Yourself »

Using the lang property, in this example, stores an upper case value in the language property:

Example

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;

Try it Yourself »

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

Note

Avoid getters or setters if you only need simple values (prevents overuse).

Object.defineProperty()

The Object.defineProperty() method can also be used to add Getters and Setters:

A Counter Example

// 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;

Try it Yourself »