Form Validation

 -- NON EMPTY FIELDS VALIDATION

 --Here is the script for validate them all--

 <script type='text/javascript'>
function notEmpty(elem, helperMsg){
	if(elem.value.length == 0){
		alert(helperMsg);
		elem.focus();
		return false;
	}
	return true;
}
</script>

 --This is the code for controllers in the form--

<form>
Required Field: <input type='text' id='req1'/>
<input type='button' 
	onclick="notEmpty

(document.getElementById('req1'), 'Please Enter a Value')"
	value='Check Field' />
</form>

-- ALL NUMBERS ONLY FIELDS 

<script type='text/javascript'>
function isNumeric(elem, helperMsg){
	var numericExpression = /^[0-9]+$/;
	if(elem.value.match(numericExpression)){
		return true;
	}else{
		alert(helperMsg);
		elem.focus();
		return false;
	}
}
</script>
<form>
Numbers Only: <input type='text' id='numbers'/>
<input type='button' 
	onclick="isNumeric

(document.getElementById('numbers'), 'Numbers Only Please')"
	value='Check Field' />
</form> 

--ALL LETTERS CHECKING FIELDS

<script type='text/javascript'>
function isAlphabet(elem, helperMsg){
	var alphaExp = /^[a-zA-Z]+$/;
	if(elem.value.match(alphaExp)){
		return true;
	}else{
		alert(helperMsg);
		elem.focus();
		return false;
	}
}
</script>
<form>
Letters Only: <input type='text' id='letters'/>
<input type='button' 
	onclick="isAlphabet

(document.getElementById('letters'), 'Letters Only Please')"
	value='Check Field' />
</form> 

--FIELD SIZE VALIDATING

<script type='text/javascript'>
function lengthRestriction(elem, min, max){
	var uInput = elem.value;
	if(uInput.length >= min && uInput.length <= max){
		return true;
	}else{
		alert("Please enter between " +min+ " and " +max+ " characters");
		elem.focus();
		return false;
	}
}
</script>
<form>
Username(6-8 characters): <input type='text' id='restrict'/>
<input type='button' 
	onclick="lengthRestriction

(document.getElementById('restrict'), 6, 8)"
	value='Check Field' />
</form>

--SELECTION BOX VALUE CHECKING

<script type='text/javascript'>
function madeSelection(elem, helperMsg){
	if(elem.value == "Please Choose"){
		alert(helperMsg);
		elem.focus();
		return false;
	}else{
		return true;
	}
}
</script>
<form>
Selection: <select id='selection'>
<option>Please Choose</option>
<option>CA</option>
<option>WI</option>
<option>XX</option>
</select>
<input type='button' 
	onclick="madeSelection

(document.getElementById('selection'), 'Please Choose Something')"
	value='Check Field' />
</form> 

--E-MAIL FIELDS CHECKING

<script type='text/javascript'>
function emailValidator(elem, helperMsg){
	var emailExp = /^[\w\-\.\+]+\@[a-zA-Z0-9\.\-]+\.[a-zA-z0-9]{2,4}$/;
	if(elem.value.match(emailExp)){
		return true;
	}else{
		alert(helperMsg);
		elem.focus();
		return false;
	}
}
</script>
<form>
Email: <input type='text' id='emailer'/>
<input type='button' 
	onclick="emailValidator1

(document.getElementById('emailer'), 'Not a Valid Email')"
	value='Check Field' />
</form> 

--ALL FORM EVENTS VALIDATING

--HTML CODE

<form onsubmit='return formValidator()' >
First Name: <input type='text' id='firstname' /><br />
Address: <input type='text' id='addr' /><br />
Zip Code: <input type='text' id='zip' /><br />
State: <select id='state'>
	<option>Please Choose</option>
	<option>AL</option>
	<option>CA</option>
	<option>TX</option>
	<option>WI</option>
</select><br />
Username(6-8 characters): <input type='text' id='username' /><br />
Email: <input type='text' id='email' /><br />
<input type='submit' value='Check Form' /><br />
</form>

--JAVASCRIPT CODE 

function formValidator(){
	// Make quick references to our fields
	var firstname = document.getElementById('firstname');
	var addr = document.getElementById('addr');
	var zip = document.getElementById('zip');
	var state = document.getElementById('state');
	var username = document.getElementById('username');
	var email = document.getElementById('email');
	
	// Check each input in the order that it appears in the form!
	if(isAlphabet(firstname, "Please enter only letters for your name")){
		if(isAlphanumeric(addr, "Numbers and Letters Only for Address")){
			if(isNumeric(zip, "Please enter a valid zip code")){
				if(madeSelection(state, "Please Choose a State")){
					if(lengthRestriction(username, 6, 8)){
						if(emailValidator

(email, "Please enter a valid email address")){
							return true;
						}
					}
				}
			}
		}
	}
	
	
	return false;
	
}

Source Link http://www.tizag.com/javascriptT/javascriptform.php