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JavaScript ES5 Object Methods


ECMAScript 5 (2009) added a lot of new Object Methods to JavaScript.


Managing Objects

// Create object with an existing object as prototype
Object.create()
// Adding or changing an object property
Object.defineProperty(object, property, descriptor)
// Adding or changing object properties
Object.defineProperties(object, descriptors)
// Accessing Properties
Object.getOwnPropertyDescriptor(object, property)
// Returns all properties as an array
Object.getOwnPropertyNames(object)
// Accessing the prototype
Object.getPrototypeOf(object)
// Returns enumerable properties as an array
Object.keys(object)

Protecting Objects

// Prevents adding properties to an object
Object.preventExtensions(object)
// Returns true if properties can be added to an object
Object.isExtensible(object)
// Prevents changes of object properties (not values)
Object.seal(object)
// Returns true if object is sealed
Object.isSealed(object)
// Prevents any changes to an object
Object.freeze(object)
// Returns true if object is frozen
Object.isFrozen(object)



Changing a Property Value

Syntax

Object.defineProperty(object, property, {value : value})

This example changes a property value:

Example

const person = {  firstName: "John", 
lastName : "Doe",  language : "EN" };// Change a propertyObject.defineProperty(person, "language",
{value : "NO"});
Try it Yourself »








Changing Meta Data
ES5 allows the following property meta data to be changed:


writable : true      // Property value can be changed
enumerable : true    // Property can be enumerated
configurable : true  // Property can be reconfigured



writable : false     // Property value can not be changed
enumerable : false   // Property can be not enumerated
configurable : false // Property can be not reconfigured


ES5 allows getters and setters to be changed:


// Defining a getter
get: function() { return language }
// Defining a setter
set: function(value) { language = value }


This example makes language read-only:


Object.defineProperty(person, "language", {writable:false});


This example makes language not enumerable:


Object.defineProperty(person, "language", {enumerable:false});



Listing All Properties
This example list all properties of an object:

Example

const person = {  firstName: "John", 
lastName : "Doe",  language : "EN" };
Object.defineProperty(person, "language", {enumerable:false});Object.getOwnPropertyNames(person);  // Returns an array of
properties
Try it Yourself »


Listing Enumerable Properties
This example list only the enumerable properties of an object:

Example

const person = {  firstName: "John", 
lastName : "Doe",  language : "EN" };
Object.defineProperty(person, "language", {enumerable:false});Object.keys(person);  // Returns an array
of enumerable
properties
Try it Yourself »


Adding a Property
This example adds a new property to an object:

Example

// Create an object:const person = {  firstName: "John",  lastName :
"Doe",  language : "EN"};// Add a propertyObject.defineProperty(person, "year",
{value:"2008"});
Try it Yourself »


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

Example

//Create an objectconst person = {firstName:"John", lastName:"Doe"};
// Define a getterObject.defineProperty(person, "fullName", {  get:
function () {return this.firstName + " " + this.lastName;}});
Try it Yourself »


A Counter Example

Example

// Define object
const 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 (i) {this.counter -= i;}});
// Play with the counter:
obj.reset;
obj.add = 5;
obj.subtract = 1;
obj.increment;
obj.decrement;

Try it Yourself »













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Reference: https://www.w3schools.com/js/js_object_es5.asp