What is if statement and how to implement in JavaScript?

If statement is the part of JavaScript. If statement executes a statement when the condition is true.

Syntax:

if (condition) {
       // block of code to be executed if the condition is true
    } 

Example:

<script type="text/javascript">

     var input = Number(prompt("Please enter a number", ""));
    if (input == 1) {
        alert("You have entered one");
    }

    if (input == 2) {
       alert("You have entered Two");
    }

    if (input == 3) {
        alert("Your have entered Three");
    }

    if (input != 1 && input != 2 && input !=3) {
        alert("Your have to enter number between 1 and 3");
    }

   </script>

Output: