JavaScript: HTML Form - checking for numbers and letters

Checking for numbers and letters

Sometimes situations arise ( suppose a user id, password or a code) when the user should fill a single or more than one field with alphabet characters (A-Z or a-z) and numbers (0-9) in an HTML form. You can write a JavaScript form validation script to check whether the required field(s) in the HTML form contains only letters and numbers.

Javascript function to check if a field input contains letters and numbers only

// Function to check letters and numbers
function alphanumeric(inputtxt)
 var letterNumber = /^[0-9a-zA-Z]+$/;
   return true;
   return false; 

To get a string contains only letters and numbers (i.e. a-z, A-Z or 0-9) we use a regular expression /^[0-9a-zA-Z]+$/ which allows only letters and numbers. Next the match() method of string object is used to match the said regular expression against the input value. Here is the complete web document.+


Flowchart: JavaScript - checking for numbers and letters


<!DOCTYPE html>
<html lang="en">
<meta charset="utf-8">
<title>JavaScript form validation - checking all letters and numbers</title>
<link rel='stylesheet' href='form-style.css' type='text/css' />
<body onload='document.form1.text1.focus()'>
<div class="mail">
<h2>Enter your Registration Number and Submit</h2>
<form name="form1" action="#">
<li><input type='text' name='text1'/></li>
<li class="rq">*Enter numbers and alphabets only.</li>
<li><input type="submit" name="submit" value="Submit" onclick="alphanumeric(document.form1.text1)" /></li>
<script src="check-letters-numbers.js"></script>

Javascript code

function alphanumeric(inputtxt)
var letters = /^[0-9a-zA-Z]+$/;
alert('Your registration number have accepted : you can try another');
return true;
alert('Please input alphanumeric characters only');
return false;

CSS Code

li {list-style-type: none;
font-size: 16pt;
.mail {
margin: auto;
padding-top: 10px;
padding-bottom: 10px;
width: 400px;
background : #D8F1F8;
border: 1px soild silver;
.mail h2 {
margin-left: 38px;
input {
font-size: 20pt;
input:focus, textarea:focus{
background-color: lightyellow;
input submit {
font-size: 12pt;
.rq {
color: #FF0000;
font-size: 10pt;

View the example in the browser

Practice the example online

See the Pen letters-numbers-field-1 by w3resource (@w3resource) on CodePen.

file_download Download the validation code from here.

Other JavaScript Validation :

Previous: JavaScript: HTML Form validation - checking for Floating point numbers
Next: JavaScript: HTML Form - restricting the length

JavaScript: Tips of the Day

|| operator

const one = false || {} || null;
const two = null || false || '';
const three = [] || 0 || true;

console.log(one, two, three);

With the || operator, we can return the first truthy operand. If all values are falsy, the last operand gets returned.
(false || {} || null): the empty object {} is a truthy value. This is the first (and only) truthy value, which gets returned. one is equal to {}.
(null || false || ""): all operands are falsy values. This means that the last operand, "" gets returned. two is equal to "".
([] || 0 || ""): the empty array[] is a truthy value. This is the first truthy value, which gets returned. three is equal to [].

Ref: https://bit.ly/3jFRBje