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

JavaScript Debugging

Errors can (will) happen, every time you write some new computer code.

Code Debugging

Programming code might contain syntax errors, or logical errors.

Many of these errors are difficult to diagnose.

Often, when programming code contains errors, nothing will happen. There are no error messages, and you will get no indications where to search for errors.

Searching for (and fixing) errors in programming code is called code debugging. Continue reading JavaScript Debugging

JavaScript JSON

JSON is a format for storing and transporting data.

JSON is often used when data is sent from a server to a web page.

What is JSON?

JSON stands for JavaScript Object Notation
JSON is a lightweight data interchange format
JSON is language independent *
JSON is “self-describing” and easy to understand

* The JSON syntax is derived from JavaScript object notation syntax, but the JSON format is text only. Code for reading and generating JSON data can be written in any programming language. Continue reading JavaScript JSON

JavaScript Modules

Modules

JavaScript modules allow you to break up your code into separate files.

This makes it easier to maintain a code-base.

Modules are imported from external files with the import statement.

Modules also rely on type="module" in the <script> tag. Continue reading JavaScript Modules