Validation types supported out of the box. All are optional, which means that all passwords are allowed by default.

• Minimum and maximum length.
• Minimum n lowercase characters (a–z).
• Minimum n uppercase characters (A–Z).
• Minimum n combined a–z and A–Z characters.
• Minimum n numeric characters (0–9).
• Minimum n special characters (characters other than a–z, A–Z, and 0–9).
• Ban particular words (tested case-insensitively).
• Ban n-length character sequences (e.g. “abc”, “XYZ”, or “789”, with a sequence length of 3; does not apply to special characters).
• Ban n-length qwerty character sequences (e.g. “qwerty” or “asdf”, with a sequence length of 4; does not apply to special characters).
• Ban sequential, identical characters (e.g. “aa” or “!!”).
• Use custom regular expressions (tested using RegExp.prototype.test) and functions (the password is provided as the first argument, and a Boolean value is expected in return).

Here's an example of how it can be used:

var password = "password";
var passed = validatePassword(password, {
  length:   [8, Infinity],
  lower:    1,
  upper:    1,
  numeric:  1,
  special:  1,
  badWords: ["password", "steven", "levithan"],
  badSequenceLength: 4
});
// passed: false

The above requires that password is at least eight characters long; has at least one lowercase, uppercase, numeric, and special character; doesn't include the words “password”, “steven”, or “levithan”; and doesn't include an alphanumeric sequence four or more characters in length (e.g. “1234”).

Here's the code (there are no external library dependencies):

http://blog.stevenlevithan.com/archives/javascript-password-validator

/*
	Password Validator 0.1
	(c) 2007 Steven Levithan <stevenlevithan.com>
	MIT License
*/
 
function validatePassword (pw, options) {
	// default options (allows any password)
	var o = {
		lower:    0,
		upper:    0,
		alpha:    0, /* lower + upper */
		numeric:  0,
		special:  0,
		length:   [0, Infinity],
		custom:   [ /* regexes and/or functions */ ],
		badWords: [],
		badSequenceLength: 0,
		noQwertySequences: false,
		noSequential:      false
	};
 
	for (var property in options)
		o[property] = options[property];
 
	var	re = {
			lower:   /[a-z]/g,
			upper:   /[A-Z]/g,
			alpha:   /[A-Z]/gi,
			numeric: /[0-9]/g,
			special: /[\W_]/g
		},
		rule, i;
 
	// enforce min/max length
	if (pw.length < o.length[0] || pw.length > o.length[1])
		return false;
 
	// enforce lower/upper/alpha/numeric/special rules
	for (rule in re) {
		if ((pw.match(re[rule]) || []).length < o[rule])
			return false;
	}
 
	// enforce word ban (case insensitive)
	for (i = 0; i < o.badWords.length; i++) {
		if (pw.toLowerCase().indexOf(o.badWords[i].toLowerCase()) > -1)
			return false;
	}
 
	// enforce the no sequential, identical characters rule
	if (o.noSequential && /([\S\s])\1/.test(pw))
		return false;
 
	// enforce alphanumeric/qwerty sequence ban rules
	if (o.badSequenceLength) {
		var	lower   = "abcdefghijklmnopqrstuvwxyz",
			upper   = lower.toUpperCase(),
			numbers = "0123456789",
			qwerty  = "qwertyuiopasdfghjklzxcvbnm",
			start   = o.badSequenceLength - 1,
			seq     = "_" + pw.slice(0, start);
		for (i = start; i < pw.length; i++) {
			seq = seq.slice(1) + pw.charAt(i);
			if (
				lower.indexOf(seq)   > -1 ||
				upper.indexOf(seq)   > -1 ||
				numbers.indexOf(seq) > -1 ||
				(o.noQwertySequences && qwerty.indexOf(seq) > -1)
			) {
				return false;
			}
		}
	}
 
	// enforce custom regex/function rules
	for (i = 0; i < o.custom.length; i++) {
		rule = o.custom[i];
		if (rule instanceof RegExp) {
			if (!rule.test(pw))
				return false;
		} else if (rule instanceof Function) {
			if (!rule(pw))
				return false;
		}
	}
 
	// great success!
	return true;
}

Whitespaces will be invalidated if you add the /[\s]/g within the custom regexes declaration. The correct regexp is /^\S+$/g