Check a number is Prime or not using JavaScript

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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