JavaScript Introduction

#javascript #html #webdev

Introduction

JavaScript is a programming language used to create dynamic content for websites.
It's an interpreted language that executes code line by line.
JavaScript is a lightweight, cross-platform[TBD], object-oriented scripting language used to make webpages interactive.

History of JavaScript

In May 1995, Brendan Eich created JavaScript, a programming language, in just 10 days.
In 1995 Netscape Communications Corporation needed a way to make web pages more interactive and dynamic.
Brendan Eich was hired by Netscape to develop a new scripting language for this purpose.
The language was initially called Mocha and later changed to LiveScript.
In December 1995, LiveScript was renamed JavaScript, partly to capitalize on the growing popularity of the programming language Java.

Variables in JavaScript

A variable is like a container that holds data that can be reused or updated later in the program.
Variables are used to store and manage data in a program.

Variables: Declared using the keywords var, let, or const.

1. var Keyword

Syntax: var variable = value;

Note: It allows it to be re-declared or updated within its scope.

Example:

var num = 5;
console.log(num);

var num = 20; // reassigning is allowed
console.log(num);

2. let Keyword

The let keyword is a modern way to declare variables in JavaScript.
It was introduced in ECMAScript 6 (ES6)[TBD].
Unlike var, let provides block-level scope and cannot be re-declared in the same scope.

Syntax: let variable = value;

Example:

let  age = 22;
age = 29; // Value can be updated
// let age = 15; //can not re-declare
console.log(age)

3. const Keyword

Syntax: let variable = value;

Example:

const pi = 3.14;
// pi = 3.20; This will throw an error
console.log(pi)

Overview of Recent Versions

ECMAScript 2025 (ES16): The current stable standard approved in June 2025. It introduces native set operations like .intersection(), .union(), and .difference().
ECMAScript 2024 (ES15): Released in 2024. It brought data grouping tools like Object.groupBy() and Map.groupBy().
ECMAScript 2023 (ES14): Released in 2023. It introduced new array manipulation capabilities like .findLast() and .toReversed().

Note: ECMAScript (ES) is the official, standardized specification for the JavaScript programming language.

What is a Compiler?

The Compiler is a translator that takes input i.e., High-Level Language, and produces an output of low-level language i.e. machine or assembly language.
The work of a Compiler is to transform the codes written in the programming language into machine code (format of 0s and 1s) so that computers can understand.

What is an Interpreter?

An Interpreter is a program that translates a programming language into a comprehensible[TBD] language.
The interpreter converts high-level language to an intermediate language[TBD].