Check password strength: Javascript

Implementation

This code snippet will return a score for the password strength. It's pure Javascript so it should work for virtually every platform and browser out there, even some mobile phones.

 
function CheckPassword(password)
{
	var strength = new Array();
	strength[0] = "Blank";
	strength[1] = "Very Weak";
	strength[2] = "Weak";
	strength[3] = "Medium";
	strength[4] = "Strong";
	strength[5] = "Very Strong";

	var score = 1;

	if (password.length < 1)
		return strength[0];

	if (password.length < 4)
		return strength[1];

	if (password.length >= 8)
		score++;
	if (password.length >= 10)
		score++;
	if (password.match(/\d+/))
		score++;
	if (password.match(/[a-z]/) &&
		password.match(/[A-Z]/))
		score++;
	if (password.match(/.[!,@,#,$,%,^,&,*,?,_,~,-,£,(,)]/))
		score++;

	return strength[score];
}
		

Usage

Call the function CheckPassword() passing the password to be checked. The result is a string representing the password strength, from "Very Weak" to "Very Strong". You can show this text in a label and also block the form if the password strength is not strong or at least medium.

You can also return the score (from 1 to 5) instead of the text, using return score instead of return strength[score].

Example

<script type="text/javascript">
	function PasswordChanged(field)
	{
		var span = document.getElementById("PasswordStrength");
		span.innerHTML = CheckPassword(field.value);
	}

	function ButtonClicked(field)
	{
		var strength = document.getElementById("PasswordStrength").innerHTML;
		
		if (strength.indexOf("Strong") < 0)
		{
			alert("Password is not strong enough!");
			return false;
		}
	}
</script>

<div>
	Password:
	<input type="text" onchange="PasswordChanged(this)" />
	<span id="PasswordStrength"></span>
	<br />
	<input type="button" value="Check" onclick="return ButtonClicked()" />
</div>