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Two text fields, only one required to be filled (either)

So I have two fields in my webpage, one for telephone number and the other for email address, I need to make either one of them required to be filled by using JavaScript NOT jQuery. Most of the answers I found here are for jQuery, any solutions with JavaScript would be much appreciated. Thanks!
function User_one(){
var phone = document.getElementById('PhoneText2').value;
var mail = document.getElementById('EmailText1').value;
if (phone && mail == ""){
alert("An error occurred.");
}else{
return false;
}
}

Update with actual code
Here's how I'd do it
(function () {
document.getElementById('myForm').addEventListener('submit', function(event){
// Get the length of the values of each input
var phone = document.getElementById('PhoneText2').value.length,
email = document.getElementById('EmailText1').value.length;
// If both fields are empty stop the form from submitting
if( phone === 0 && email === 0 ) {
event.preventDefault();
}
}, false);
})();
Since you haven't supplied any code for us to work with, I'll answer in pseudo-code:
On form submission {
If (both telephone and email is empty) {
throw validation error
}
otherwise {
submit the form
}
}
If you show me your code I'll show you mine :-)

Need to validate with range and by pass validation function with session value if user want to enter value beyond range

I have multiple input type text on jsp form for each the range is defined to the next input type textbox i want to validate with the defined range and if the value beyond the range validation function ask for pop confirmation if user enter userid in text that compare with session value ie 'user' then the validation function allow user to submit form with return true and not ask again for that filed validate .how can i achieve this using javascript function.any other way that can i achieve same using javascript .Request you to Suggest Option with example code.
JavaScript code:-
if(document.getElementById('pH'+formid).value !=0)
{
var user;
var value=document.getElementById('pH'+formid).value;
var maxmin=document.getElementById('pHspecf'+formid).value.split('-');
var max=maxmin[0];
var min=maxmin[1];
if(value<min||value>mix)
{
alert("max-"+max+" min-"+min+" value of parameter-"+value);
var c=confirm("Entered Value Beyond the Specification Range.\n DO you Still Want To continue Press Yes..!");
if (c==true)
{
var person=prompt("Please enter your Username","Your User name");
if (person!=null)
{user=person;
alert("Hello "+person+" Your Request Is Accepted..!");
}else{
document.getElementById('pH'+formid).style.backgroundColor = "lightblue";
document.getElementById('pH'+formid).focus();
return false;
}
}
else
{
document.getElementById('pH'+formid).focus();
return false;
}
}
}

Is there a way to reverse the suspension of form-submission or will it be better not to have it done in the first place?

I am trying to make a simple web application. In my login page I have a form with a text field, a password and a submit button. Form submission is prevented if either fields are empty. This is the script I use:
function checkLoginCredentials() {
var usernameFormValue = $("#usernameForm").val().trim();
var passwordFormValue = $("#passwordForm").val().trim();
var validated;
$("#loginForm").submit(function(event){
if (usernameFormValue === "" || passwordFormValue === "") {
$("span").html("Enter a username or password");
validated = false
} else {
validated = true;
}
return validated;
});
}
However, I noticed that once the script runs and form submission is prevented, the user can no longer make an attempt to log in again. The only alternative I can think of is to have ALL validations done by my login servlet and utility classes. Is there a way around this or must validations of invalid entries like empty strings be done by my Java Classes?

The issue here is how you are assigning the validation code. You have a checkLoginCredentials and when you call it you read the form values. And than you add a form submission. You should add the reading of the textbox values inside of the submit method, not outside.
$("#loginForm").submit(function(event){
var usernameFormValue = $("#usernameForm").val().trim(),
passwordFormValue = $("#passwordForm").val().trim(),
validated;
if (usernameFormValue === "" || passwordFormValue === "") {
$("span").html("Enter a username or password");
validated = false
} else {
validated = true;
}
return validated;
});

Javascript Validation Form

I am working with a form that has a catcha image. When a user fills out the form, and presses submit ( and only when the captcha number is wrong) the fields are reset or cleared. How can I prevent this from happening?
If a visitor fills out the form, presses submit, the expected behaviour is theform is submitted, or if the captch number is wrong, retain the information that the visitor had input in the fields and ask the visitor to fill in the correct captcha number...
Here is the js:
function MM_validateForm() { //v4.0
if (document.getElementById){
var i,p,q,nm,test,num,min,max,errors='',args=MM_validateForm.arguments;
for (i=0; i<(args.length-2); i+=3) { test=args[i+2]; val=document.getElementById(args[i]);
if (val) { nm=val.name; if ((val=val.value)!="") {
if (test.indexOf('isEmail')!=-1) { p=val.indexOf('#');
if (p<1 || p==(val.length-1)) errors+='- '+nm+' must contain an e-mail address.\n';
} else if (test!='R') { num = parseFloat(val);
if (isNaN(val)) errors+='- '+nm+' must contain a number.\n';
if (test.indexOf('inRange') != -1) { p=test.indexOf(':');
min=test.substring(8,p); max=test.substring(p+1);
if (num<min || max<num) errors+='- '+nm+' must contain a number between '+min+' and '+max+'.\n';
} } } else if (test.charAt(0) == 'R') errors += '- '+nm+' is required.\n'; }
} if (errors) alert('The following error(s) occurred:\n'+errors);
document.MM_returnValue = (errors == '');
} }

When you want to prevent the default behaviour you've to use a callback function like this:
function onsubmit_handler(evt) {
if (/* validation is ok */) {
return true;
}
else { /* validation is not ok */
evt.preventDefault();
return false;
}
}
yourfom.onsubmit = onsubmit_handler;

Am I correct in believing that the captcha is validated (only) on the server after a successful validation by the JS (i.e., not via an Ajax call in the form submission event handler)? Am I further correct in believing that you're doing a true HTML form submission instead of an Ajax form submission in the background?
If both of those are true, then the problem probably isn't in your JavaScript at all (I say "probably" only because you could conceivably have a JS function that clears all the form fields on load or something like that). You're submitting the form to the server, the server looks at the captcha, sees that the answer is wrong, and displays the form again -- with blank values. You need to change your server code to include the user's previous answers as value attributes (or selected options or whatever as appropriate for the element type) when it writes the form after a server-side validation failure.

JS validation error firing even when no value is being entered

I have a problem where I have 3 input fields. The first field is for the username and the other two fields are for password validation. Now the password fields cannot contain the user name field so I have written the logic to display a message if the password fields contains any part of the user name. However if the user name field has nothing in it, that same validation message is still firing if something is typed in the password field.
Here is the code
Code getting the user name field:
if (document.getElementById("tUserName")) {
uN = document.getElementById("tUserName").value;
}
else {
uN = "";
}
The user name field regEx:
containsUsername = new RegExp(uN);
this is the code that is responsible for the validation error message:
if (document.getElementByIdd("tUserName")) {
if (containsUsername.test(value)) {
dojo.addClass(dojo.byId('result-userName'), 'hide');
}
else {
dojo.removeClass(dojo.byId('result-userName'), 'hide');
}
}

I'm worried that I must be missing the point here so bear with me if I am....
So you want the validation error not to show when they type in passwords without anything in the username field?
Can you not just check that the username has a value of something other than an empty string before you try running it through the regex?
if (document.getElementById("tUserName")) {
if (document.getElementById("tUserName").value != '' && containsUsername.test(value)) {
dojo.addClass(dojo.byId('result-userName'), 'hide');
}
else {
dojo.removeClass(dojo.byId('result-userName'), 'hide');
}
}