Object Protection Methods

// Prevents re-assignment
const car = {type:"Fiat", model:"500", color:"white"};

// Prevents adding object properties
Object.preventExtensions(object)

// Returns true if properties can be added to an object
Object.isExtensible(object)

// Prevents adding and deleting object properties
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)

Using const

The most common way to protect an object from being changed is by using the const keyword.

With const you can not re-assign the object, but you can still change the value of a property, delete a property or create a new property. Continue reading JavaScript Object Protection

JavaScript Accessors (Getters and Setters)

ECMAScript 5 (ES5 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:
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;

JavaScript Setter (The set Keyword)

This example uses a lang property to set the value of the language property. Continue reading JavaScript Object Accessors

Property Management Methods

// Adding or changing an object property
Object.defineProperty(object, property, descriptor)

// Adding or changing object properties
Object.defineProperties(object, descriptors)

// Accessing a Property
Object.getOwnPropertyDescriptor(object, property)

// Accessing Properties
Object.getOwnPropertyDescriptors(object)

// Returns all properties as an array
Object.getOwnPropertyNames(object)

// Accessing the prototype
Object.getPrototypeOf(object)

JavaScript Object.defineProperty()

The Object.defineProperty() method can be used to:

Adding a new property to an object
Changing property values
Changing property metadata
Changing object getters and setters

Continue reading JavaScript Object Properties

General Methods

// Copies properties from a source object to a target object
Object.assign(target, source)

// Creates an object from an existing object
Object.create(object)

// Returns an array of the key/value pairs of an object
Object.entries(object)

// Creates an object from a list of keys/values
Object.fromEntries()

// Returns an array of the keys of an object
Object.keys(object)

// Returns an array of the property values of an object
Object.values(object)

// Groups object elements according to a function
Object.groupBy(object, callback)

JavaScript Object.assign()

The Object.assign() method copies properties from one or more source objects to a target object. Continue reading JavaScript Object Methods

JavaScript Object Prototypes

All JavaScript objects inherit properties and methods from a prototype.

In the previous article we learned how to use an object constructor:

Example

function Person(first, last, age, eyecolor) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eyecolor;
}

const myFather = new Person("John", "Doe", 50, "blue");
const myMother = new Person("Sally", "Rally", 48, "green");

We also learned that you can not add a new property to an existing object constructor : Continue reading JavaScript Object Prototypes

JavaScript Object Definition

Methods for Defining JavaScript Objects

Using an Object Literal
Using the new Keyword
Using an Object Constructor
Using Object.assign()
Using Object.create()
Using Object.fromEntries()

JavaScript Object Literal

An object literal is a list of property names:values inside curly braces {}.

{firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};

Note:

An object literal is also called an object initializer.

Continue reading JavaScript Object Definition

JavaScript Reserved Words

In JavaScript you cannot use these reserved words as variables, labels, or function names:

abstract	arguments	await*	boolean
break	byte	case	catch
char	class*	const*	continue
debugger	default	delete	do
double	else	enum*	eval
export*	extends*	false	final
finally	float	for	function
goto	if	implements	import*
in	instanceof	int	interface
let*	long	native	new
null	package	private	protected
public	return	short	static
super*	switch	synchronized	this
throw	throws	transient	true
try	typeof	var	void
volatile	while	with	yield

Words marked with* was new in ECMAScript 5 and ECMAScript 6. Continue reading JavaScript Reserved Words

Reduce Activity in Loops

Loops are often used in programming.

Each statement in a loop, including the for statement, is executed for each iteration of the loop.

Statements or assignments that can be placed outside the loop will make the loop run faster. Continue reading JavaScript Performance

JavaScript Common Mistakes

This chapter points out some common JavaScript mistakes.

Accidentally Using the Assignment Operator

JavaScript programs may generate unexpected results if a programmer accidentally uses an assignment operator (=), instead of a comparison operator (==) in an if statement. Continue reading JavaScript Common Mistakes

JavaScript Style Guide

Always use the same coding conventions for all your JavaScript projects.

JavaScript Coding Conventions

Coding conventions are style guidelines for programming. They typically cover:

Naming and declaration rules for variables and functions.
Rules for the use of white space, indentation, and comments.
Programming practices and principles.

Coding conventions secure quality:

Improve code readability
Make code maintenance easier

Coding conventions can be documented rules for teams to follow, or just be your individual coding practice.

This page describes the general JavaScript code conventions used by W3Schools.
You should also read the next chapter “Best Practices”, and learn how to avoid coding pitfalls.

Continue reading JavaScript Style Guide