Variables

Variables are the containers for storing values or expressions They are used to store data temporarily in the computer

Example

section = "3U"
console.log(section)

⚖️ Rules for js variables

• Case sensitive
• Must start with an an alphabet or underscore
• Cannot start with a number
• Cannot use reserved words as variables
• Should be meaningful
• Cannot contain space or hyphen (-)

Here are few examples:

• score ✅
• _id ✅
• 01 🚫
• await 🚫

📢 Declaration of varaibles

There are three methods of declaring a variable in js

• let keyword
• const keyword
• var keyword

Keyword	Access	Assignment	Initialise
let	{...}	Reassignable	Optional
const	{...}	Final	Required
var	function	Reassignable	Optional

Reassignment

let count = 0
count = 1 //This works

const count = 0
count = 1 //This doesn't work

var count = 0
count = 1 //This works

Accessibility

{
  let blockVariable = "I am hidden";
  var functionVariable = "I am visible";
}

console.log(blockVariable);    //This doesn't work
console.log(functionVariable); //This works

Declearing multiple variables

// Both works
let name="Rohan" , role="Student";

let name="Rohan";
let role="Student";   

Note

• If you assign values to variables that have not yet been declared, the variables will automatically be declared.

  x = 120; //  No error here

• "var" has some confusing behaviors regarding scope and hoisting, so modern developers generally avoid it in favor of let and const.