<?php
$mynumber= rand(673,62389);
echo $mynumber;
?>

<script type="text/javascript">
//defining variable and storinging in script
var randomnumber= <?= $mynumber?>;
// Validating
function CheckData()
{
with(document.mail)
{
if(q.value != randomnumber)
{
alert("Please Enter Correct Number");
q.focus();
return false;
}
}
return true;
}
</script>

<form name="mail" action="go.php" method="post" onsubmit="return CheckData()">
<input type="text" name="q">
<input type="submit" name="Submit" value="Submit">
</form>

function isValidEmail(str) {
return (str.indexOf(".") > 2) && (str.indexOf("@") > 0);
}
function CheckData()
{
if (document.getElementById('abc').style.display == "block")
document.getElementById('abc').style.display = "none";
with(document.mailform)
{
name.value = trim(name.value);
phone.value = trim(phone.value);
if(name.value == "")
{
document.getElementById('abc').style.display = "block";
document.getElementById('one').innerText = "Please Enter Your First Name";
name.focus();
return false;
}
}
return true;
}
function trim(sValue)
{
	if (sValue == null)
		return null;
	for (var i = 0; sValue.charAt(i) == " "; i ++);
	sValue = sValue.substring(i,sValue.length);
	if (sValue == null)
		return null;
	for(var i = (sValue.length-1); sValue.charAt(i) == " "; i --);
	return sValue.substring(0, (i + 1));
}

<script type="text/javascript" src="validate.js"></script>

<div id="abc" style="display:none; color:#FF0000;">

<script language = "Javascript">
// Declaring required variables
var digits = "0123456789";
// non-digit characters which are allowed in phone numbers
var phoneNumberDelimiters = "()- ";
// characters which are allowed in international phone numbers
// (a leading + is OK)
var validWorldPhoneChars = phoneNumberDelimiters + "+";
// Minimum no of digits in an international phone no.
var minDigitsInIPhoneNumber = 10; function isInteger(s)
{ var i;
for (i = 0; i < s.length; i++)
{
// Check that current character is number.
var c = s.charAt(i);
if (((c < "0") || (c > "9"))) return false;
}
// All characters are numbers.
return true;
}
 
function stripCharsInBag(s, bag)
{ var i;
var returnString = "";
// Search through string's characters one by one.
// If character is not in bag, append to returnString.
for (i = 0; i < s.length; i++)
{
// Check that current character isn't whitespace.
var c = s.charAt(i);
if (bag.indexOf(c) == -1) returnString += c;
}
return returnString;
}
 
function checkInternationalPhone(strPhone){
s=stripCharsInBag(strPhone,validWorldPhoneChars);
return (isInteger(s) && s.length >= minDigitsInIPhoneNumber);
}
 
function ValidateForm(){
var Phone=document.frmSample.txtPhone
 
if ((Phone.value==null)||(Phone.value=="")){
alert("Please Enter your Phone Number")
Phone.focus()
return false
}
if (checkInternationalPhone(Phone.value)==false){
alert("Please Enter a Valid Phone Number")
Phone.value=""
Phone.focus()
return false
}
return true
}
</script>

<form name="frmSample" method="post" action="#" onSubmit="return ValidateForm()">
<p>Enter a phone number :
<input type="text" name="txtPhone">
</p>
<p>
<input type="submit" name="Submit" value="Submit">
</p>
</form>