# How to Check If Number is Prime in Javascript

In this tutorial, you will learn how to check if number is prime in javascript. The number which is divisible only by itself and 1 is known as a prime number. For example 7, 11, 13, 17, etc.

Detecting whether a number is prime or not is very easy, but it can be tricky if the number is coming from an input field because the value present in the input field is of string type. So first, we have to convert it into a number type using the `Number()` method and then perform any sort of calculations.

There are numerous ways to find whether a number is prime or not. But for the sake of simplicity, we will create a custom method to verify that. It mainly involves the usage of `for` loop and modulus (`%`) operator.

In the following example, we will enter a random number in the input field. Upon click of a button, we will check whether the number is prime or not and display the result on the screen.  Please have a look over the code example and the steps given below.

HTML & CSS

• We have 4 elements in the HTML file (`div`, `input`, `button`, and `h1`). The `div` element is just a wrapper for the rest of the elements.
• The `innerText` for the `button` element is `“Get”` and for the `h1` element, it is `“Result”`.
• We have done some basic styling using CSS and added the link to our `style.css` stylesheet inside the `head` element.
• We have also included our javascript file `script.js` with a `script` tag at the bottom.
```<!DOCTYPE html>
<html lang="en">

<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>

<body>

<div class="container">
<input type="number" placeholder="Enter Number">
<button>Get</button>
<h1>Result</h1>
</div>

<script src="script.js"></script>
</body>

</html>```
```.container {
text-align: center;
}

button {
margin-top: 10px;
}

input {
display: block;
margin: 10px auto;
}

input[type=number]::-webkit-inner-spin-button,
input[type=number]::-webkit-outer-spin-button {
-webkit-appearance: none;
margin: 0;
}```

Javascript

• We have selected the `input` element, `button` element, and `h1` element using the `document.querySelector()` method and stored them in `input`, `btnGet`, and `output` variables respectively.
• We have attached a `click` event listener to the `button` element.
• In the event handler function, we are getting value from the `input` element using `value` property. We are converting it into number type using the `Number()` method and storing it in the `num` variable.
• We have the `isPrime()` method which will take a number as a parameter. It will verify whether the number is prime or not and will return a Boolean value.
• We are calling the `isPrime()` method and passing `num` as a parameter. Depending upon the returned Boolean value, we will assign `“Yes”` or `“No”` to the `result` variable.
• We are displaying the `result` in the `h1` element using the `innerText` property.
```let input = document.querySelector("input");
let btnGet = document.querySelector("button");
let output = document.querySelector("h1");