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

JavaScript: function and arguments

const person = {
  name: 'Lydia Hallie',
  hobbies: ['coding'],

function addHobby(hobby, hobbies = person.hobbies) {
  return hobbies;

addHobby('running', []);
addHobby('baking', person.hobbies);


The addHobby function receives two arguments, hobby and hobbies with the default value of the hobbies array on the person object.
First, we invoke the addHobby function, and pass "running" as the value for hobby and an empty array as the value for hobbies. Since we pass an empty array as the value for y, "running" gets added to this empty array.
Then, we invoke the addHobby function, and pass "dancing" as the value for hobby. We didn't pass a value for hobbies, so it gets the default value, the hobbies property on the person object. We push the hobby dancing to the person.hobbies array.
Last, we invoke the addHobby function, and pass "bdaking" as the value for hobby, and the person.hobbies array as the value for hobbies. We push the hobby baking to the person.hobbies array.
After pushing dancing and baking, the value of person.hobbies is ["coding", "dancing", "baking"]

Ref: https://bit.ly/2Hcpkm6