April 25, 2022

How to Check if a Field Input Contains Numbers Only in Javascript

By Krishnaa JavaScript Questions 0 Comments

In this tutorial, you will learn how to check if a field input contains numbers only in javascript. A number is formed by the combination of digits from 0 to 9. Input element is suitable for a single line text content and textarea element is suitable for multiline text content. From a developer perspective, it can be a bit tricky to find if a field input contains numbers only.

There are numerous ways to check if a field input contains numbers only. But for the sake of simplicity, we will use the regular expression and ternary operator (?) to accomplish our goal. The test() method of RegExp object is used to perform a pattern search in a string and returns a Boolean value.

In the following example, we have one input field where we will enter some random text. Upon click of a button, we will check if the field input contains numbers only 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 “Check” 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">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <link rel="stylesheet" href="style.css">
  <title>Document</title>
</head>

<body>

  <div class="container">    
    <input type="text" />
    <button>Check</button>
    <h1>Result</h1>
  </div>

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

</html>

.container {        
  text-align: center;
}

button {
margin-top: 10px;
padding: 10px 20px;
}

input {
display: block;
padding: 5px 10px;
margin: auto;
}

Javascript

We have selected the button element, input element, and h1 element using the document.querySelector() method and stored them in btnCheck, inputEl, and output variables respectively.
We have attached a click event listener to the button element.
We have the regExp variable which holds a regular expression /^\d+$/ as its value.
In the event handler function, we are getting value from the input element and storing it in the value variable.
We are calling the test() method of regExp and passing value as a parameter. It will return a Boolean value which we are storing in the hasNumbers variable.
We are using the ternary operator (?) and checking whether hasNumbers is true or false. If it is true, that means the field input contains numbers only.
Depending upon the result of the check, we will assign “Yes” or “No” to the result variable.
We are displaying the result in the h1 element using the innerText property.

let btnCheck = document.querySelector("button");
let inputEl = document.querySelector("input");
let output = document.querySelector("h1");

let regExp = /^\d+$/;

btnCheck.addEventListener("click", () => {
  let value = inputEl.value;
  let hasNumbers = regExp.test(value)
  let result = hasNumbers ? "Yes" : "No";
  output.innerText = result;
});

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