Check a number is Prime or not using JavaScript

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.



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<!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>

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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.

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<!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>                                

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Output:

  • Before checking the number:
  • After checking the number:


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