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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]+$/;
 if((inputtxt.value.match(letterNumber)) 
  {
   return true;
  }
else
  { 
   alert("message"); 
   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:

Flowchart: JavaScript - checking for numbers and letters

HTML Code

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

Javascript code

function alphanumeric(inputtxt)
{ 
var letters = /^[0-9a-zA-Z]+$/;
if(inputtxt.value.match(letters))
{
alert('Your registration number have accepted : you can try another');
document.form1.text1.focus();
return true;
}
else
{
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

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JavaScript: Tips of the Day

valid Email

const createMember = ({ email, address = {}}) => {
	const validEmail = /.+\@.+\..+/.test(email)
	if (!validEmail) throw new Error("Valid email pls")

	return {
		email,
		address: address ? address : null
	}
}

const member = createMember({ email: "[email protected]" })
console.log(member)

The default value of address is an empty object {}. When we set the variable member equal to the object returned by the createMember function, we didn't pass a value for address, which means that the value of address is the default empty object {}. An empty object is a truthy value, which means that the condition of the address ? address : null conditional returns true. The value of address is the empty object {}.

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