JavaScript Let & Const

Modern JavaScript

About Lesson

In this JavaScript lesson we are going to learn about JavaScript Let & Const, as you know JavaScript is a scripting language that was introduced for building web pages alive and interactive with the user. JavaScript is also , often abbreviated as JS, is a programming language that conforms to the ECMAScript specification. JavaScript is high-level, often just-in-time compiled, and multi-paradigm. It has curly-bracket syntax, dynamic typing, prototype-based object-orientation, and first-class functions.

What is ES ?

In the year 1996, a standards organization called ECMA (European Computer Manufacturers Association) International carved out standard specification called ECMAScript (ES) which all browser vendors could implement. And Javascript is the most well-known implementations of ES.

Versions of ES ?

Name	Year	Description
ES1	1997	It was the first edition of Modern JavaScript
ES2	1998	Editorial changes only
ES3	1999	Regular expressions and try/catch added
ES4	Null	This version was not released because of some issues.
ES5	2009	Added some new features like use strict, isArray, foreach, map, filter, reduce and some more.
ES6	2015	Some new features has been added, that we will talk about this.
ES7	2016	Some new features has been added, that we will talk about this.
ES8	2017	Some new features has been added, that we will talk about this.
ES9	2018	Changes in RegEx and Rest or Spread Properties
ES10	2019	Some new features has been added
ES11	2020	Some new features has been added

JavaScript ES6

ES6 was one of the best progress of JavaScript in recent years. after introducing ES6, the modern programming was introduced in JavaScript.

Let & Const (JavaScript ES6)

Before this in JavaScript we had function and global scope, after introduction of let and const now JS has block scope, and it was a feature in JavaScript ES6.

let num = 5;

if(num < 6 ) {

    let greeting = "Hello ";
    let greeting = "World";
    console.log(greeting);

}

let num = 5;

if(num < 6 ) {

let greeting = "Hello ";

let greeting = "World";

console.log(greeting);

}

const num = 5;

if(num < 6 ) {

    const greeting = "Hello ";
    const greeting = "World";
    console.log(greeting);

}

const num = 5;

if(num < 6 ) {

const greeting = "Hello ";

const greeting = "World";

console.log(greeting);

}