Variables

There are 3 ways to declare variable in JS/TS.

Variable Type	Block/Global Scope	Can be updated	Can be re-declare
var	Global	Y	Y
let	Block	Y	X
const	Block	X	X

You can check the simple explanation for each variable types.

var

var str = "var-a"

var str = "var-c" // Can be re-declare
str = "var-b" // Can be updated

console.log(str) // should be "var-b"

let

let str = "let-a"

let str = "let-c" // Error cannot be re-declare X
str = "let-b" // Can be updated

console.log(str) // should be "let-b"

const

const str = "const-a"

const str = "const-c" // Error cannot be re-declare
str = "const-b" // Error cannot be updated

console.log(str) // should be "const-a"