Check a number is Prime or not using JavaScript

Last Updated : 15 Jul, 2019

A prime number is a number that is divisible by 1 and itself only. First few prime numbers are: 2, 3, 5, 7, 11, 13, 17, …
A JavaScript uses the DOM model to check the input number is prime or not and display its corresponding alert message on the screen.

Examples:

Input : 4
Output : Not Prime

Input : 5
Output : Prime

Example 1: This example display the result by using alert function.

<!DOCTYPE html> 
<html> 
  
<head> 
    <title> 
        Check a number is Prime or 
        not using JavaScript 
    </title> 
      
    <script type="text/javascript"> 
      
        // Function to check prime number 
        function p() { 
              
            var n, i, flag = true; 
              
            // Getting the value form text 
            // field using DOM 
            n = document.myform.n.value; 
            n = parseInt(n) 
            for(i = 2; i <= n - 1; i++) 
                if (n % i == 0) { 
                    flag = false; 
                    break; 
                } 
                  
                // Check and display alert message 
            if (flag == true) 
                alert(n + " is prime"); 
            else
                alert(n + " is not prime"); 
        } 
    </script> 
</head> 
  
<body> 
    <center> 
        <h1>GeeksforGeeks</h1> 
          
        <h4>check number is prime or not</h4> 
          
        <hr color="Green"> 
          
        <form name="myform"> 
            Enter the number: 
            <input type="text" name=n value=""> 
              
            <br><br> 
              
            <input type="button" value="Check" onClick="p()"> 
            <br> 
        </form> 
    </center> 
</body> 
  
</html> 

Output:

Before checking the number:
After checking the number:

Example 2: This example checks a given number is prime or not and display result on the console.

<!DOCTYPE html> 
<html> 
  
<head> 
    <title> 
        Check a number is Prime or 
        not using JavaScript 
    </title> 
      
    <style> 
        body { 
            border:2px solid black; 
            width:400px; 
            height:150px; 
            text-align:center; 
        } 
        h1 { 
            color:green; 
        } 
    </style> 
      
    <script type="text/javascript"> 
      
        // Function to check for prime number 
        function checkPrime() { 
              
            var n, i, flag = true; 
              
            // Getting the value form the 
            // text field using DOM 
            n = document.myform.n.value; 
            n = parseInt(n) 
            for (i = 2; i <= n - 1; i++) 
                if (n % i == 0) { 
                    flag = false; 
                    break; 
                } 
                  
            // Check and display output 
            if (flag == true) 
                console.log(n + " is prime"); 
            else
                console.log(n + " is not prime"); 
        } 
    </script> 
</head> 
  
<body> 
        <h1>GeeksforGeeks</h1> 
        <h4>check number is prime or not</h4> 
      
        <form name="myform"> 
            Enter the number: 
            <input type="text" name=n value=""> 
            <input type="button" value="Check" onClick="checkPrime()"> 
            <br> 
        </form> 
    </center> 
</body> 
  
</html>                                 

Output:

Before checking the number:
After checking the number:

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