<!-- validate username & password-->
function validateUNPW(inputValue, id){
var includeText = "01234567890qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM!@."
var includeTextSplitted = includeText.split("");
var inputTextSplitted = inputValue.split("");
var error = new Array();

	for (i=0;i<inputTextSplitted.length;i++){
		error[i] = 'y';
	}
	for (x=0;x<inputTextSplitted.length;x++){
		for (y=0;y<includeTextSplitted.length;y++){
			if (inputTextSplitted[x] == includeTextSplitted[y]){
				error[x] = 'n';
			}			
		}
	}
	for (i=0;i<inputTextSplitted.length;i++){
		if (error[i] == 'y'){
			alert("You have entered a character that's not allowed!");	
			field = "";
			document.getElementById(id).value=field;
			break;
		}
	}
}
<!-- validate username & password-->


<!-- validateText-->
function validateText(inputValue, id){
var includeText = " 'qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM"
var includeTextSplitted = includeText.split("");
var inputTextSplitted = inputValue.split("");
var error = new Array();

	for (i=0;i<inputTextSplitted.length;i++){
		error[i] = 'y';
	}
	for (x=0;x<inputTextSplitted.length;x++){
		for (y=0;y<includeTextSplitted.length;y++){
			if (inputTextSplitted[x] == includeTextSplitted[y]){
				error[x] = 'n';
			}			
		}
	}
	for (i=0;i<inputTextSplitted.length;i++){
		if (error[i] == 'y'){
			alert("Please enter a correct value!");	
			field = "";
			document.getElementById(id).value=field;
			break;
		}
	}
}
<!--***end*** validateText-->


<!-- validateNumber-->
function validateNumber(inputValue, id){
var includeText = "0123456789"
var includeTextSplitted = includeText.split("");
var inputTextSplitted = inputValue.split("");
var error = new Array();

	for (i=0;i<inputTextSplitted.length;i++){
		error[i] = 'y';
	}
	for (x=0;x<inputTextSplitted.length;x++){
		for (y=0;y<includeTextSplitted.length;y++){
			if (inputTextSplitted[x] == includeTextSplitted[y]){
				error[x] = 'n';
			}			
		}
	}
	for (i=0;i<inputTextSplitted.length;i++){
		if (error[i] == 'y'){
			alert("Please enter an integer");	
			field = "";
			document.getElementById(id).value=field;			
			break;
		}
	}
}
<!--***end*** validateNumber-->


<!-- validateEmail-->
function validateEmail(inputValue, id){
var includeText = "@.";
var includeTextSplitted = includeText.split("");
var inputTextSplitted = inputValue.split("");
var pass_count = 0;

	for (x=0;x<inputTextSplitted.length;x++){
		for (y=0;y<includeTextSplitted.length;y++){
			if (inputTextSplitted[x] == includeTextSplitted[y]){
				pass_count ++;
			}			
		}
	}
		
		//error message if @ or . is missing
		if (pass_count < 2){
			alert("Please enter a valid e-mail address");	
			field = "";
			document.getElementById(id).value=field;
		}
	
}
<!--***end*** validateEmail-->


<!-- checkillegalcharacters-->
function checkillegalcharacters(inputValue, id){
var illegalText = "><";
var illegalTextSplitted = illegalText.split("");
var inputTextSplitted = inputValue.split("");
var illegal_count = 0;

	for (x=0;x<inputTextSplitted.length;x++){
		for (y=0;y<illegalTextSplitted.length;y++){
			if (inputTextSplitted[x] == illegalTextSplitted[y]){
				illegal_count ++;
			}			
		}
	}
		
		//error message if @ or . is missing
		if (illegal_count > 0){
			alert("Please enter again");	
			field = "";
			document.getElementById(id).value=field;
		}
	
}
<!--***end*** checkillegalcharacters-->


function validateForm(){
	with(document.contact_form){
		if(your_contact_email.value == ""){
			alert("Please enter your email address.");
			your_contact_email.focus();
			return false;
		} else if(your_first_name.value == ""){
			alert("Please enter your first name.");
			your_first_name.focus();
			return false;
		} else if(your_last_name.value == ""){
			alert("Please enter your last name.");
			your_last_name.focus();
			return false;
		}else {
			return true;
		}
	}
}


function validateForm2(){
	with(document.share){
		if(email_friend_your_email.value == ""){
			alert("Please enter the email address.");
			email_friend_your_email.focus();
			return false;
		} else if(email_friend_friends_email.value == ""){
			alert("Please enter the email address.");
			email_friend_friends_email.focus();
			return false;
		}else {
			return true;
		}
	}
}