JavaScript: HTML Form - IP address validation

IP address validation

Every computer connected to the Internet is identified by a unique four-part string, known as its Internet Protocol (IP) address. An IP address consists of four numbers (each between 0 and 255) separated by periods. The format of an IP address is a 32-bit numeric address written as four decimal numbers (called octets) separated by periods; each number can be written as 0 to 255 (e.g., to

Example of valid IP address


Example of invalid IP address

  • 210.110 – must have 4 octets
  • 255 – must have 4 octets
  • y.y.y.y – the only digit has allowed
  • 255.0.0.y – the only digit has allowed
  • 666.10.10.20 – digit must between [0-255]
  • 4444.11.11.11 – digit must between [0-255]
  • 33.3333.33.3 – digit must between [0-255]

JavaScript code to validate an IP address

function ValidateIPaddress(ipaddress) 
 if (/^(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/.test(myForm.emailAddr.value))
    return (true)
alert("You have entered an invalid IP address!")
return (false)

Explanation of the said Regular expression (IP address)

Regular Expression Pattern :

Character Description
/ .. / All regular expressions start and end with forward slashes.
^ Matches the beginning of the string or line.
25[0-5] Matches 250 or 251 or 252 or 253 or 254 or 255.
| or
2[0-4][0-9] Start with 2, follow a single character between 0-4 and again a single character between 0-9.
| or
? Matches the previous character 0 or 1 time.
[0-9][0-9] Matches a single character between 0-9 and again a single character between 0-9.
? Matches the previous character 0 or 1 time.
\. Matches the character "." literally.

Note: Last two parts of the regular expression is similar to above.

Syntax diagram - IP-address validation:

Syntax diagram - IP-address validation

Let apply the above JavaScript function in an HTML form.


<!DOCTYPE html>
<html lang="en">
<meta charset="utf-8">
<title>JavaScript form validation - checking IP address/title>
<link rel='stylesheet' href='form-style.css' type='text/css' />
<body onload='document.form1.text1.focus()'>
<div class="mail">
<h2>Input an IP address and Submit</h2>
<form name="form1" action="#"> 
<li><input type='text' name='text1'/></li>
<li class="submit"><input type="submit" name="submit" value="Submit" onclick="ValidateIPaddress(document.form1.text1)"/></li>
<script src="ipaddress-validation.js"></script>

JavaScript Code

function ValidateIPaddress(inputText)
 var ipformat = /^(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/;
 return true;
 alert("You have entered an invalid IP address!");
return false; } }


Flowchart : JavaScript - ipaddress validation

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 Javascript IP address validation in the browser

file_download Download the validation code from here.

Other JavaScript Validation:

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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