JS Var vs Let difference

The difference between var and let in JavaScript is block scope.

var

When a var is declared outside a block scope, and then re declared inside a block after the first declaration. The value of the var gets changed after the block scope is over.

//first declaration of var x
 var x=10;
 {
     //second declaration of var x
     var x=5;
     alert(x); //prints 5
 }
 alert(x); //prints 5

let

However by using let keyword to declare a variable. the value of the variable doesn't get changed by the subsequent re declaration inside the block.

//first declaration of let var y
 let y=15;
 {
     //second declaration of let var y
     let y=90;
     alert(y); //prints 90
 }
 alert(y); //prints 15