Skip to content
Related Articles

Related Articles

Improve Article
Save Article
Like Article

Difference between var and let in JavaScript

  • Difficulty Level : Basic
  • Last Updated : 20 Jul, 2021

var and let are both used for variable declaration in javascript but the difference between them is that var is function scoped and let is block scoped.
It can be said that a variable declared with var is defined throughout the program as compared to let.
An example will clarify the difference even better
Example of var:

Input:
console.log(x);
var x=5;
console.log(x);
Output:
undefined
5


Example of let:

Hey geek! The constant emerging technologies in the world of web development always keeps the excitement for this subject through the roof. But before you tackle the big projects, we suggest you start by learning the basics. Kickstart your web development journey by learning JS concepts with our JavaScript Course. Now at it's lowest price ever!

Input:
console.log(x);
let x=5;
console.log(x);
Output:
Error


Let’s see code in JavaScript:
Code #1:




<html>
  
<body>
    <script>
        // calling x after definition
        var x = 5;
        document.write(x, "\n");
  
        // calling y after definition 
        let y = 10;
        document.write(y, "\n");
  
        // calling var z before definition will return undefined
        document.write(z, "\n");
        var z = 2;
  
        // calling let a before definition will give error
        document.write(a);
        let a = 3;
    </script>
</body>
  
</html>                            

Output



Code #2:
In the following code, clicking start will call a function that changes the color of the two headings every 0.5sec. The color of first heading is stored in a var and the second one is declared by using let.
Both of them are then accessed outside the function block. Var will work but the variable declared using let will show an error because let is block scoped.




<!DOCTYPE html>
<html>
  
<head>
    <title>Var vs Let</title>
</head>
  
<body>
  
    <h1 id="var" style="color:black;">GeeksForGeeks</h1>
    <h1 id="let" style="color:black;">GeeksForGeeks</h1>
    <button id="btn" onclick="colour()">Start</button>
    <!-- executing function on button click -->
  
    <script type="text/javascript">
        function colour() {
  
            setInterval(function() {
  
                if (document.getElementById('var').style.color == 'black')
                    var col1 = 'blue';
                else
                    col1 = 'black';
  
                // setting value of color 1 through var
  
                if (document.getElementById('let').style.color == 'black') {
                    let col2 = 'red';
                } else {
                    col2 = 'black';
                }
  
                // setting value of color 2 through let
  
                document.getElementById('var').style.color = col1;
  
                document.getElementById('let').style.color = col2;
  
                // changing color of h1 in html
            }, 500);
  
        }
    </script>
</body>
  
</html>

Output:

JavaScript is best known for web page development but it is also used in a variety of non-browser environments. You can learn JavaScript from the ground up by following this JavaScript Tutorial and JavaScript Examples.




My Personal Notes arrow_drop_up
Recommended Articles
Page :

Start Your Coding Journey Now!