JavaScript Object.defineProperty()

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Example

Add a property:

// Create an Object:
const person = {
firstName: "John",
lastName: "Doe",
language: "EN"
};

// Add a new Property
Object.defineProperty(person, "year", {value:"2008"})

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Change a property:

// Create an object:
const person = {
firstName: "John",
lastName: "Doe",
language: "EN"
};

// Change a property
Object.defineProperty(person, "language", {value:"NO"})

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More Examples Below !

Description

The Object.defineProperty() method adds or changes an object property.

The Object.defineProperty() method lets you change property metadata.

The Object.defineProperty() method lets you add getters and setters.

See more example below.

Related Methods:

Object.defineProperty() adds or changes one property.

Object.defineProperties() adds or changes many properties.

Object.getOwnPropertyNames() returns the property names of an object.

Object.getOwnPropertyDescriptor() returns the descriptor of a property.

Object.getOwnPropertyDescriptors() returns the descriptors of all properties.

Syntax

Object.defineProperty(object, property, descriptor)

Parameters

Parameter Description

object Required.
The object.

property Required.
The property name.

descriptor Required.
A descriptor of the property to be added or changed:

value: value
writable : true|false
enumerable : true|false
configurable : true|false
get : function
set : function

Return Value

Type Description

Object The passed object with the changes made.

More Examples

Example

// Create an Object:
const person = {
firstName: "John",
lastName : "Doe",
language : "NO",
};

// Change a Property:
Object.defineProperty(person, "language", {
value: "EN",
writable : true,
enumerable : true,
configurable : true
});

// Enumerate Properties
let txt = "";
for (let x in person) {
txt += person[x] + "<br>";
}

// Display Properties
document.getElementById("demo").innerHTML = txt;

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Next example is the same code, except it hides the language property from enumeration:

Example

// Create an Object:
const person = {
firstName: "John",
lastName : "Doe",
language : "NO",
};

// Change a Property:
Object.defineProperty(person, "language", {
value: "EN",
writable : true,
enumerable : false,
configurable : true
});

// Enumerate Properties
let txt = "";
for (let x in person) {
txt += person[x] + "<br>";
}
document.getElementById("demo").innerHTML = txt;

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Setters and Getters

This example creates a setter and a getter to secure upper case updates of language:

Example

// Create an Object:
const person = {
firstName: "John",
lastName : "Doe",
language : "NO"
};

// Change a Property:
Object.defineProperty(person, "language", {
get : function() { return language },
set : function(value) { language = value.toUpperCase()}
});

// Change Language
person.language = "en";

// Display Language
document.getElementById("demo").innerHTML = person.language;

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This example uses a getter to join first name and last name:

Example

// Create an Object:
const person = {
firstName: "John",
lastName : "Doe"
};

// Define a Getter
Object.defineProperty(person, "fullName", {
get: function () {return this.firstName + " " + this.lastName;}
});

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JavaScript Getters and Setters are perfect for creating counters:

Example

// 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;}
});

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