function sololetras(which)
{
	var valido = "\"'";
	if(document.images)
	{
		for (var i = 0; i < which.length; i++)
		{
			var tempobj = which.elements[i];
			if (tempobj.type == "text" || tempobj.type == "textarea" || tempobj.type == "password")
			{
				for (var j = 0; j < tempobj.value.length; j++)
				{
					var ok = "yes";
					temp = tempobj.value.substring(j, j+1);
					if (valido.indexOf(temp) == "-1")
					{
						ok = "no";
					}
					if (ok == "yes")
					{
						alert("No debe ingresar comillas simples o dobles (" + tempobj.id + ")");
						tempobj.focus();
						tempobj.select();
						return false;
					}
				}
			}
		}
	}
}

function requerido(campo, forma, idioma)
{
	var lleno = true;
	if(campo.value == "")
	{
		lleno = false;
	}
	if (!lleno)
	{
		alert("Asegurese que el campo " + campo.name + " ha sido llenado");
		return false;		
	}
	else
	{
		forma.submit();
		return true;
	}
}

function validarn(field)
{
	var valid = "0123456789."
	var ok = "yes";
	var temp;
	
	for (var i = 0; i < field.value.length; i++)
	{
		temp = "" + field.value.substring(i, i+1);
		if (valid.indexOf(temp) == "-1") ok = "no";
	}
	if (ok == "no")
	{
		alert("Debe ingresar solo números.");
		field.focus();
		field.select();
	}
}
function validarnRif(field)
{
	var valid = "0123456789VEJPG"
	var ok = "yes";
	var temp;
	
	for (var i = 0; i < field.value.length; i++)
	{
		temp = "" + field.value.substring(i, i+1);
		if (valid.indexOf(temp) == "-1") ok = "no";
	}
	if (ok == "no")
	{
		alert("Debe ingresar Letra y números.\nFormato: 'Letra ID + Número + Dígito Verificador' sin usar separadores.\nEjm: J000688028");
		field.focus();
		field.select();
	}
}

function nochr(field)
{
	var valid = "0123456789.ABCDEFGHIJKLMNOPQRSTVWXYZ,abcdefghijklmnopqrstvwxyz \""
	var ok = "yes";
	var temp;
	for (var i=0; i<field.value.length; i++)
	{
		temp = "" + field.value.substring(i, i+1);
		if (valid.indexOf(temp) == "-1")
		{
			ok = "no";
		}
	}
	if (ok == "no")
	{
		alert("Por favor, no introduzca caracteres especiales");
		field.focus();
		field.select();
	}
}

function enviar_form(forma)
{
	for (var i = 0; i < forma.length; i++)
	{
		var objeto = forma.elements[i];
		if (objeto.id == "required")
		{
			if (objeto.value.length == "0")
			{
				alert("Los campos marcados con asterisco (*) deben ser Ingresados");
				return false;
			}
		}
		if (objeto.id == "combo")
		{
			if (objeto.value == 0 || objeto.value == "")
			{
				alert("Los campos marcados con asterisco (*) deben ser Ingresados");
				return false;
			}
		}
	}
}
function emailCheck (emailStr,campo) {
var emailPat=/^(.+)@(.+)$/
var specialChars="\\(\\)<>@,;:\\\\\\\"\\.\\[\\]"
var validChars="\[^\\s" + specialChars + "\]"
var quotedUser="(\"[^\"]*\")"
var ipDomainPat=/^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/
var atom=validChars + '+'
var word="(" + atom + "|" + quotedUser + ")"
var userPat=new RegExp("^" + word + "(\\." + word + ")*$")
var domainPat=new RegExp("^" + atom + "(\\." + atom +")*$")

var matchArray=emailStr.match(emailPat)
if (matchArray==null) {
	alert("Error, la direccion de correo es incorrecta")
	return false
}
var user=matchArray[1]
var domain=matchArray[2]

if (user.match(userPat)==null) {
    // user is not valid
    alert("Error, la direccion de correo es incorrecta")
    return false
}

var IPArray=domain.match(ipDomainPat)
if (IPArray!=null) {
    // this is an IP address
	  for (var i=1;i<=4;i++) {
	    if (IPArray[i]>255) {
	        alert("Error, la direccion de correo es incorrecta")
		return false
	    }
    }
    return true
}

var domainArray=domain.match(domainPat)
if (domainArray==null) {
	alert("Error, la direccion de correo es incorrecta")
    return false
}

var atomPat=new RegExp(atom,"g")
var domArr=domain.match(atomPat)
var len=domArr.length
if (domArr[domArr.length-1].length<2 || 
    domArr[domArr.length-1].length>3) {
   alert("Error, la direccion de correo es incorrecta")
   return false
}

if (len<2) {
   alert("Error, la direccion de correo es incorrecta")
   return false
   
}

return true;
}

//credit card validation***********************************************************************************************************

<!-- Begin
var Cards = new makeArray(8);
Cards[0] = new CardType("MasterCard", "51,52,53,54,55", "16");
var MasterCard = Cards[0];
Cards[1] = new CardType("VisaCard", "4", "13,16");
var VisaCard = Cards[1];
Cards[2] = new CardType("AmExCard", "34,37", "15");
var AmExCard = Cards[2];
Cards[3] = new CardType("DinersClubCard", "30,36,38", "14");
var DinersClubCard = Cards[3];
Cards[4] = new CardType("DiscoverCard", "6011", "16");
var DiscoverCard = Cards[4];
Cards[5] = new CardType("enRouteCard", "2014,2149", "15");
var enRouteCard = Cards[5];
Cards[6] = new CardType("JCBCard", "3088,3096,3112,3158,3337,3528", "16");
var JCBCard = Cards[6];
var LuhnCheckSum = Cards[7] = new CardType();

/*************************************************************************\
CheckCardNumber(form)
function called when users click the "check" button.
\*************************************************************************/
function CheckCardNumber(form) {
var tmpyear;
if (form.CardNumber.value.length == 0) {
alert("Please enter a Card Number.");
form.CardNumber.focus();
return;
}
if (form.ExpYear.value.length == 0) {
alert("Please enter the Expiration Year.");
form.ExpYear.focus();
return;
}
if (form.ExpYear.value > 96)
tmpyear = "19" + form.ExpYear.value;
else if (form.ExpYear.value < 21)
tmpyear = "20" + form.ExpYear.value;
else {
alert("The Expiration Year is not valid.");
return;
}
tmpmonth = form.ExpMon.options[form.ExpMon.selectedIndex].value;
// The following line doesn't work in IE3, you need to change it
// to something like "(new CardType())...".
// if (!CardType().isExpiryDate(tmpyear, tmpmonth)) {
if (!(new CardType()).isExpiryDate(tmpyear, tmpmonth)) {
alert("This card has already expired.");
return;
}
card = form.CardType.options[form.CardType.selectedIndex].value;
var retval = eval(card + ".checkCardNumber(\"" + form.CardNumber.value +
"\", " + tmpyear + ", " + tmpmonth + ");");
cardname = "";
if (retval)



// comment this out if used on an order form
alert("This card number appears to be valid.");


else {
// The cardnumber has the valid luhn checksum, but we want to know which
// cardtype it belongs to.
for (var n = 0; n < Cards.size; n++) {
if (Cards[n].checkCardNumber(form.CardNumber.value, tmpyear, tmpmonth)) {
cardname = Cards[n].getCardType();
break;
   }
}
if (cardname.length > 0) {
alert("This looks like a " + cardname + " number, not a " + card + " number.");
}
else {
alert("This card number is not valid.");
      }
   }
}
/*************************************************************************\
Object CardType([String cardtype, String rules, String len, int year, 
                                        int month])
cardtype    : type of card, eg: MasterCard, Visa, etc.
rules       : rules of the cardnumber, eg: "4", "6011", "34,37".
len         : valid length of cardnumber, eg: "16,19", "13,16".
year        : year of expiry date.
month       : month of expiry date.
eg:
var VisaCard = new CardType("Visa", "4", "16");
var AmExCard = new CardType("AmEx", "34,37", "15");
\*************************************************************************/
function CardType() {
var n;
var argv = CardType.arguments;
var argc = CardType.arguments.length;

this.objname = "object CardType";

var tmpcardtype = (argc > 0) ? argv[0] : "CardObject";
var tmprules = (argc > 1) ? argv[1] : "0,1,2,3,4,5,6,7,8,9";
var tmplen = (argc > 2) ? argv[2] : "13,14,15,16,19";

this.setCardNumber = setCardNumber;  // set CardNumber method.
this.setCardType = setCardType;  // setCardType method.
this.setLen = setLen;  // setLen method.
this.setRules = setRules;  // setRules method.
this.setExpiryDate = setExpiryDate;  // setExpiryDate method.

this.setCardType(tmpcardtype);
this.setLen(tmplen);
this.setRules(tmprules);
if (argc > 4)
this.setExpiryDate(argv[3], argv[4]);

this.checkCardNumber = checkCardNumber;  // checkCardNumber method.
this.getExpiryDate = getExpiryDate;  // getExpiryDate method.
this.getCardType = getCardType;  // getCardType method.
this.isCardNumber = isCardNumber;  // isCardNumber method.
this.isExpiryDate = isExpiryDate;  // isExpiryDate method.
this.luhnCheck = luhnCheck;// luhnCheck method.
return this;
}

/*************************************************************************\
boolean checkCardNumber([String cardnumber, int year, int month])
return true if cardnumber pass the luhncheck and the expiry date is
valid, else return false.
\*************************************************************************/
function checkCardNumber() {
var argv = checkCardNumber.arguments;
var argc = checkCardNumber.arguments.length;
var cardnumber = (argc > 0) ? argv[0] : this.cardnumber;
var year = (argc > 1) ? argv[1] : this.year;
var month = (argc > 2) ? argv[2] : this.month;

this.setCardNumber(cardnumber);
this.setExpiryDate(year, month);

if (!this.isCardNumber())
return false;
if (!this.isExpiryDate())
return false;

return true;
}
/*************************************************************************\
String getCardType()
return the cardtype.
\*************************************************************************/
function getCardType() {
return this.cardtype;
}
/*************************************************************************\
String getExpiryDate()
return the expiry date.
\*************************************************************************/
function getExpiryDate() {
return this.month + "/" + this.year;
}
/*************************************************************************\
boolean isCardNumber([String cardnumber])
return true if cardnumber pass the luhncheck and the rules, else return
false.
\*************************************************************************/
function isCardNumber() {
var argv = isCardNumber.arguments;
var argc = isCardNumber.arguments.length;
var cardnumber = (argc > 0) ? argv[0] : this.cardnumber;
if (!this.luhnCheck())
return false;

for (var n = 0; n < this.len.size; n++)
if (cardnumber.toString().length == this.len[n]) {
for (var m = 0; m < this.rules.size; m++) {
var headdigit = cardnumber.substring(0, this.rules[m].toString().length);
if (headdigit == this.rules[m])
return true;
}
return false;
}
return false;
}

/*************************************************************************\
boolean isExpiryDate([int year, int month])
return true if the date is a valid expiry date,
else return false.
\*************************************************************************/
function isExpiryDate() {
var argv = isExpiryDate.arguments;
var argc = isExpiryDate.arguments.length;

year = argc > 0 ? argv[0] : this.year;
month = argc > 1 ? argv[1] : this.month;

if (!isNum(year+""))
return false;
if (!isNum(month+""))
return false;
today = new Date();
expiry = new Date(year, month);
if (today.getTime() > expiry.getTime())
return false;
else
return true;
}

/*************************************************************************\
boolean isNum(String argvalue)
return true if argvalue contains only numeric characters,
else return false.
\*************************************************************************/
function isNum(argvalue) {
argvalue = argvalue.toString();

if (argvalue.length == 0)
return false;

for (var n = 0; n < argvalue.length; n++)
if (argvalue.substring(n, n+1) < "0" || argvalue.substring(n, n+1) > "9")
return false;

return true;
}

/*************************************************************************\
boolean luhnCheck([String CardNumber])
return true if CardNumber pass the luhn check else return false.
Reference: http://www.ling.nwu.edu/~sburke/pub/luhn_lib.pl
\*************************************************************************/
function luhnCheck() {
var argv = luhnCheck.arguments;
var argc = luhnCheck.arguments.length;

var CardNumber = argc > 0 ? argv[0] : this.cardnumber;

if (! isNum(CardNumber)) {
return false;
  }

var no_digit = CardNumber.length;
var oddoeven = no_digit & 1;
var sum = 0;

for (var count = 0; count < no_digit; count++) {
var digit = parseInt(CardNumber.charAt(count));
if (!((count & 1) ^ oddoeven)) {
digit *= 2;
if (digit > 9)
digit -= 9;
}
sum += digit;
}
if (sum % 10 == 0)
return true;
else
return false;
}

/*************************************************************************\
ArrayObject makeArray(int size)
return the array object in the size specified.
\*************************************************************************/
function makeArray(size) {
this.size = size;
return this;
}

/*************************************************************************\
CardType setCardNumber(cardnumber)
return the CardType object.
\*************************************************************************/
function setCardNumber(cardnumber) {
this.cardnumber = cardnumber;
return this;
}

/*************************************************************************\
CardType setCardType(cardtype)
return the CardType object.
\*************************************************************************/
function setCardType(cardtype) {
this.cardtype = cardtype;
return this;
}

/*************************************************************************\
CardType setExpiryDate(year, month)
return the CardType object.
\*************************************************************************/
function setExpiryDate(year, month) {
this.year = year;
this.month = month;
return this;
}

/*************************************************************************\
CardType setLen(len)
return the CardType object.
\*************************************************************************/
function setLen(len) {
// Create the len array.
if (len.length == 0 || len == null)
len = "13,14,15,16,19";

var tmplen = len;
n = 1;
while (tmplen.indexOf(",") != -1) {
tmplen = tmplen.substring(tmplen.indexOf(",") + 1, tmplen.length);
n++;
}
this.len = new makeArray(n);
n = 0;
while (len.indexOf(",") != -1) {
var tmpstr = len.substring(0, len.indexOf(","));
this.len[n] = tmpstr;
len = len.substring(len.indexOf(",") + 1, len.length);
n++;
}
this.len[n] = len;
return this;
}

/*************************************************************************\
CardType setRules()
return the CardType object.
\*************************************************************************/
function setRules(rules) {
// Create the rules array.
if (rules.length == 0 || rules == null)
rules = "0,1,2,3,4,5,6,7,8,9";
  
var tmprules = rules;
n = 1;
while (tmprules.indexOf(",") != -1) {
tmprules = tmprules.substring(tmprules.indexOf(",") + 1, tmprules.length);
n++;
}
this.rules = new makeArray(n);
n = 0;
while (rules.indexOf(",") != -1) {
var tmpstr = rules.substring(0, rules.indexOf(","));
this.rules[n] = tmpstr;
rules = rules.substring(rules.indexOf(",") + 1, rules.length);
n++;
}
this.rules[n] = rules;
return this;
}