JavaScript: HTML Form - IP address validation

Last update on August 19 2022 21:50:37 (UTC/GMT +8 hours)

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., 0.0.0.0 to 255.255.255.255).

Example of valid IP address

115.42.150.37
192.168.0.1
110.234.52.124

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 :

/^(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]?)$/

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
[01]
?	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:

Let apply the above JavaScript function in an HTML form.

HTML Code

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

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]?)$/;
 if(inputText.value.match(ipformat))
 {
 document.form1.text1.focus();
 return true;
 }
 else
 {
 alert("You have entered an invalid IP address!");
 document.form1.text1.focus();
return false;
 }
 }

Flowchart:

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

Download the validation code from here.

Other JavaScript Validation:

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