Difference between var let and constant

In any programming language, variables are named containers containing any type of data at a specific memory location. The name of every variable must be unique.

In JavaScript, we can create a variable in 3 ways :

using var -

var name; // only declaration
var fname = Ansh; // declaration and initialization

using let -

let name; // only declaration
let fname = Ansh; // declaration and initialization

using const - We cannot use const without setting a value. i.e. const can't be undefined.

const name = Ansh; // declaration and initialization

We can use any of the above ways to declare variables. But is there any difference between these? let's see

Var is function scope but let and const are block scope.

<html>
    <head>
        <title>let vs const vs var</title>
    </head>
    <body>
        <script>
            function cart(){
                var item1 = "milk";
                console.log(item1);
                if(true){     //let and const life exist only in this block.
                    const budget= 500;
                    let item2 = "butter";
                    console.log(budget);
                    console.log(item1);// var can be accessed here
                }
                console.log(item2);// we can't access item2 here because it is accessible only in 'if' block. This line will give error.
            }
            cart();
        </script>
    </body>
</html>

OUTPUT:

Output

We can't change the value of const but let and var values can be updated.

<html>
    <head>
        <title>let vs const vs var</title>
    </head>
    <body>
        <script>
            let myName="Ansh";
            var myAge=22;
            myName="Shriansh";// No need to declare again
            myAge=21;// No need to declare again
            console.log(myName);
            console.log(myAge);
        </script>
    </body>
</html>

OUTPUT: You can see the updated values on the console.

Output

<html>
    <head>
        <title>let vs const vs var</title>
    </head>
    <body>
        <script>
            const myFname="Shriansh Kumar";
            myFname="Kumar";
            console.log(myFname);
        </script>
    </body>
</html>

OUTPUT: It will give an error.

Output

Different ways to declare variables in JavaScript