Variable

Variable is a contener that stores data and save it to memoey location.

There are 3 types of variable’s in JavaScript var, let, const

Syntex:

const variable_name;
let x = 100
var y = 200
Keyword Description
var Try to avoid using it because of the block scoping issue.
let Introduced in ES6 (2015). Variables declared with let have block scope and must be declared before use.
const Once declared, const variables cannot be reassigned or modified.

Let’s see a Example:

const accountId = 4303;
let accountEmail = "demo@gmail.com";
var accountPass = "123456";
accountCity = "Kolkata"; // not a good practice
let accountState;

// console.log() is use to print in console;

console.log(accountId);
console.log(accountEmail);
console.log(accountPass);
console.log(accountCity);
console.log(accountState);

Output:

4303
demo@gmail.com
123456
Kolkata
undefined

Change data of variable:

accountEmail = "octaveweb@gmail.com";
accountPass = "123910";
accountState = "West Bangal";

console.log(accountEmail);
console.log(accountPass);
console.log(accountState);

Output:

octaveweb@gmail.com
123910
West Bangal

See some Error’s

const accountId = 4303;
console.log(accountId);

Output:

4030;

But if we that to assign

const accountId = 4303;
console.log(accountId);
accountId = 20; // ❌ Error: Assignment to constant variable.

Output:

Error: Assignment to constant variable.

Use let insted of const if you know the value might change in futute