Develop Reference

How to Trigger Validation

How do I force a user to enter a valid time and valid number before pressing the button "Show"?
I have two fields in my html code and I found two good validation scripts in JS. One for time and one to determine if input field has a numeric value.
I can't change anything in the HTML.
function checkTime() {
re = /^\d{1,2}:\d{2}([ap]m)?$/;
if (time_untilopt.value != '' && !time_untilopt.value.match(re)) {
alert("Wrong time!");
return false;
}
}
function checkRoomNr() {
var numbers = /^[0-9]+$/;
if (roomopt.value.match(numbers)) {
console.log("is number");
} else {
console.log("not a number!");
}
}
<div>
<label for="time-until">Time</label>
<input type="text" id="time-until">
</div>
<div>
<label for="room">Room</label>
<input type="text" id="room">
</div>
<button id="show-schedule">Show</button>

If you want the validation to take place as data is being entered into the fields, you should set your functions up to run on the input event of the fields. If you want to wait until the user leaves the field and has made changes to the value of the field, then you can use the change event of the fields.
But, you'll also want the data to be checked when the form that contains the fields is submitted, so you need to set up a submit event handler for the form as well.
The way to connect a function to an event is to register the function as an "event handler" and that is done (using modern standards-based code) with the .addEventListener() method:
// First, get references to the elements you'll want to work with.
// And, use those variable names to reference the elements in your
// code, not their IDs.
var timeUntil = document.getElementById("time-until");
var room = document.getElementById("room");
var form = document.querySelector("form");
// We'll set up a variable to keep track of whether there are any errors
// and we'll assume that there are not any initially
var valid = true;
// Set up the event handling functions:
timeUntil.addEventListener("change", checkTime);
room.addEventListener("change", checkRoomNr);
form.addEventListener("submit", validate);
function checkTime(evt){
re = /^\d{1,2}:\d{2}([ap]m)?$/;
if(timeUntil.value != '' && !timeUntil.value.match(re)) {
console.log("Wrong time!");
valid = false; // Indicate an error
} else {
valid = true;
}
}
function checkRoomNr(evt){
var numbers = /^[0-9]+$/;
if(!room.value.match(numbers)){
console.log ("not a number!");
valid = false; // Indicate an error
} else {
valid = true;
}
}
// This function is called when the form is submitted
function validate(evt){
// Invoke the validation functions in case the fields have not been checked yet
checkTime();
checkRoomNr();
if(!valid){
evt.preventDefault(); // Cancel the form's submission
console.log("Submission cancelled due to invalid data");
}
}
<form action="#">
<div>
<label for="time-until">Time</label>
<input type="text" id="time-until">
</div>
<div>
<label for="room">Room</label>
<input type="text" id="room">
<div>
<button id="show-schedule">Show</button>
<form>

function checkTime( val ) { //Pass a value
return /^\d{1,2}:\d{2}([ap]m)?$/.test( val ); //Return a boolean
}
function checkNum( val ) { //Pass a value
return /^\d+$/.test( val ); //Return a boolean
}
const time = document.getElementById("time-until"),
room = document.getElementById("room"),
show = document.getElementById("show-schedule");
function validateForm () {
show.disabled = (checkTime( time.value ) && checkNum( room.value )) === false;
}
[time, room].forEach( el => el.addEventListener("input", validateForm) );
<div>
<label for="time-until">Time</label>
<input type="text" id="time-until">
</div>
<div>
<label for="room">Room</label>
<input type="text" id="room">
</div>
<!-- MAKE BUTTON DISABLED -->
<button id="show-schedule" disabled>Show</button>
Now you can reuse your functions like checkTime( val ) regardless of the input ID.

This may be a starting point basically you need to add event handlers and wire up time_untiloptand time_untilopt and add disabled to the show button. and listen for changes. There many ways, this is just an idea.
const button = document.getElementById('show-schedule');
const time_untilopt = document.getElementById('time-until');
const roomopt = document.getElementById('room');
function checkTime() {
re = /^\d{1,2}:\d{2}([ap]m)?$/;
if (time_untilopt.value != '' && !time_untilopt.value.match(re)) {
alert("Wrong time!");
return false;
}
return true;
}
function checkRoomNr() {
var numbers = /^[0-9]+$/;
if (roomopt.value.match(numbers)) {
console.log("is number");
return true;
} else {
console.log("not a number!");
return false;
}
}
function change() {
button.disabled = !(checkTime() && checkRoomNr());
}
<div>
<label for="time-until">Time</label>
<input type="text" id="time-until" onchange="change()">
</div>
<div>
<label for="room">Room</label>
<input type="text" id="room" onchange="change()">
</div>
<button id="show-schedule" disabled="true">Show</button>

Inside both of your functions you'll want to set up your variables (time_untilopt and roomopt) to actually point to your two <input> fields. Then you'll simply want to return true if they pass validation, and return false if they don't.
To trigger these checks, you'll want to set up an onlick attribute for your submission, which is tied in to a third function, which I have named show(). This third function should conditionally check that both of the other functions return true. If they do, all is good, and you can continue with the submission. If they're not good, simply return false in this function as well.
This can be seen in the following:
function checkTime() {
re = /^\d{1,2}:\d{2}([ap]m)?$/;
var time_untilopt = document.getElementById('time-until');
if (time_untilopt.value != '' && !time_untilopt.value.match(re)) {
return true;
}
else {
console.log("Wrong time!");
return false;
}
}
function checkRoomNr() {
var numbers = /^[0-9]+$/;
var roomopt = document.getElementById('room');
if (roomopt.value.match(numbers)) {
return true;
} else {
console.log("The room number is not a number!");
return false;
}
}
function show() {
if (checkTime() && checkRoomNr()) {
console.log('Both validations passed!');
return true;
}
else {
return false;
}
}
<div>
<label for="time-until">Time</label>
<input type="text" id="time-until">
</div>
<div>
<label for="room">Room</label>
<input type="text" id="room">
</div>
<button id="show-schedule" onclick="show()">Show</button>
Also note that your checkTime() function is actually doing the exact opposite of what you want; if the time is not empty and matches the validation, you want to return true, not false. This has been corrected in the above example.
Hope this helps! :)

Form Validation Vanilla JS

I'm building a multipage form and I have some unusual validation requirements. Here's what I'd like to do/what I have done so far.
What I Want to Do:
(1) As each form field is filled in, I want a function to run and check that the user-input has met certain conditions -- i.e. for first and last name, that there are no numbers and there is a space in between the names.
(2) Once each of the field are full and have passed as true, I want another function to run that re-enabled a previously disabled "Next" button that will move the user to the next page of the form.
What I Have Done
(1) Created a mini version of the form with two inputs:
One that takes a first name, a space and a last name
One that takes a phone number set up the following way xxx xxx xxx
(2) I've console.logged the results with pass/fail logic so I know when certain things are being input by the user, that the code is validating properly.
Where I am Stuck:
I do not know how to create the secondary code that will reenabled the previously disabled "next" button that will move the form to the next page.
What I would like to do is make it so when the "Next" button is reenabled, and clicked on, it's own onclick function hides the current page, looks for the next page in the sequence and changes its display:block and I believe I have that code worked out separately, but I don't know how to integrate it with my other needs.
function checkForm()
{
var firstName = document.getElementById("name").value;
var phone = document.getElementById("phone").value;
function checkFirstName()
{
if(firstName == "" || !isNaN(firstName) || !firstName.match(/^[A-Za-z]*\s{1}[A-Za-z]*$/))
{
console.log("Put a first Name and Last Name");
}
else
{
console.log("Thank You");
}
};
checkFirstName();
function checkPhoneNumber()
{
if(!phone.match(/^[0-9]*\s{1}[0-9]*\s{1}[0-9]*$/))
{
console.log("Please Put in a proper phone number");
}
else
{
console.log("Thank you");
cansubmit = true;
}
};
checkPhoneNumber();
};
<form>
First Name: <input type="text" id="name" onblur="checkForm()" /><label id="nameErrorPrompt"></label>
<br />
Phone Number: <input type="text" id="phone" onblur="checkForm()" /><label></label>
<br />
<button id="myButton" disabled="disabled">Test Me</button>
</form>

See below code.
It might be more user-friendly to use on keyup rather than onblur, as most users I know will try and click the disabled button, rather than pressing tab or focusing on another element.
function checkForm() {
var firstName = document.getElementById("name").value;
var phone = document.getElementById("phone").value;
var phoneCanSubmit, nameCanSubmit = false;
function checkFirstName() {
if (firstName == "" || !isNaN(firstName) || !firstName.match(/^[A-Za-z]*\s{1}[A-Za-z]*$/)) {
nameCanSubmit = false;
console.log("Put a first Name and Last Name");
} else {
nameCanSubmit = true;
console.log("Thank You");
}
};
checkFirstName();
function checkPhoneNumber() {
if (!phone.match(/^[0-9]*\s{1}[0-9]*\s{1}[0-9]*$/)) {
phoneCanSubmit = false;
console.log("Please Put in a proper phone number");
} else {
phoneCanSubmit = true;
console.log("Thank you");
cansubmit = true;
}
};
checkPhoneNumber();
if (nameCanSubmit && phoneCanSubmit) {
document.getElementById("myButton").disabled = false;
} else {
document.getElementById("myButton").disabled = true;
}
};
<form>
First Name:
<input type="text" id="name" onblur="checkForm()" />
<label id="nameErrorPrompt"></label>
<br />Phone Number:
<input type="text" id="phone" onblur="checkForm()" />
<label></label>
<br />
<button id="myButton" disabled="disabled">Test Me</button>
</form>

The code below gives you what you want. I removed some extraneous checks to simplify the code and also moved the event handlers from he HTML to the JavaScript. I also pulled the field checks out of the larger checkForm function. This provides you the flexibility to use them one at at time if need be.
window.addEventListener('load', function(e) {
var nameInput = document.getElementById('name');
var phoneInput = document.getElementById('phone');
var myButton = document.getElementById('myButton');
myButton.addEventListener('click', function(e) {
e.preventDefault(); //Stop the page from refreshing
getNextPage('Next page shown!!');
}, false);
nameInput.addEventListener('blur', function(e) {
checkName(this.value);
}, false);
phoneInput.addEventListener('blur', function(e) {
//Uncomment below to make this responsible only for checking the phone input
//checkPhoneNumber(this.value);
/*You could do away with diasbling and check the form
on submit, but if you want to keep the disable logic
check the whole form on the blur of the last item*/
checkForm();
}, false);
}, false);
function getNextPage(foo) {
console.log('Callback fired: ', foo);
//Do something here
}
function checkPhoneNumber(phone) {
if(!phone.match(/^[0-9]*\s{1}[0-9]*\s{1}[0-9]*$/)) {
console.log("Please Put in a proper phone number");
return 0;
}
else {
console.log("Thank you name entered");
return 1;
}
};
//Removed a bit of over coding, no ned to check isNaN or empty string since using regex already
function checkName(firstAndLastName) {
if(!firstAndLastName.match(/^[A-Za-z]*\s{1}[A-Za-z]*$/)) {
console.log("Put a first Name and Last Name");
return 0;
}
else {
console.log("Thank You phone entered");
return 1;
}
};
function checkForm() {
var validCount = 0;
fieldCount = document.forms[0].elements.length - 1; //substract one for the submitbutton!
var phoneNum = document.getElementById('phone').value;
var name = document.getElementById('name').value;
var myButton = document.getElementById('myButton');
validCount += checkPhoneNumber(phoneNum);
validCount += checkName(name);
console.log(validCount + ' of ' + fieldCount + ' fields are valid');
if (validCount > 0 && validCount === fieldCount) {//Compare the inputs to the number of valid inputs
myButton.disabled = false;
}
else {
myButton.disabled = true;
}
}
HTML
<form>
First Name: <input type="text" id="name" /><label id="nameErrorPrompt"></label>
<br />
Phone Number: <input type="text" id="phone" /><label></label>
<br />
<button id="myButton" disabled="disabled">Test Me</button>
</form>

How about you start by making the onblur for each input return a boolean indicating if the field is valid.
Then setting a cansubmit variable (= checkName && checkPhone) in the checkForm function and only moving on after that - then you don't need to enable and disable the button.
If you really want the button to enable you can use the same pattern, but do
document.getElementById("myButton").disabled = !canSubmit;
and you will always want to call checkForm on field blur like you are now.
Also note you aren't scoping canSubmit locally right now.

Validating a checkbox after already validating other sections of a form [duplicate]

I have a form with multiple checkboxes and I want to use JavaScript to make sure at least one is checked. This is what I have right now but no matter what is chosen an alert pops up.
JS (wrong)
function valthis(){
if (document.FC.c1.checked) {
alert ("thank you for checking a checkbox")
} else {
alert ("please check a checkbox")
}
}
HTML
<p>Please select at least one Checkbox</p>
<br>
<br>
<form name = "FC">
<input type = "checkbox" name = "c1" value = "c1"/> C1
<br>
<input type = "checkbox" name = "c1" value = "c2"/> C2
<br>
<input type = "checkbox" name = "c1" value = "c3"/> C3
<br>
<input type = "checkbox" name = "c1" value = "c4"/> C4
<br>
</form>
<br>
<br>
<input type = "button" value = "Edit and Report" onClick = "valthisform();">
So what I ended up doing in JS was this:
function valthisform(){
var chkd = document.FC.c1.checked || document.FC.c2.checked||document.FC.c3.checked|| document.FC.c4.checked
if (chkd == true){
} else {
alert ("please check a checkbox")
}
}
I decided to drop the "Thank you" part to fit in with the rest of the assignment. Thank you so much, every ones advice really helped out.

You should avoid having two checkboxes with the same name if you plan to reference them like document.FC.c1. If you have multiple checkboxes named c1 how will the browser know which you are referring to?
Here's a non-jQuery solution to check if any checkboxes on the page are checked.
var checkboxes = document.querySelectorAll('input[type="checkbox"]');
var checkedOne = Array.prototype.slice.call(checkboxes).some(x => x.checked);
You need the Array.prototype.slice.call part to convert the NodeList returned by document.querySelectorAll into an array that you can call some on.

This should work:
function valthisform()
{
var checkboxs=document.getElementsByName("c1");
var okay=false;
for(var i=0,l=checkboxs.length;i<l;i++)
{
if(checkboxs[i].checked)
{
okay=true;
break;
}
}
if(okay)alert("Thank you for checking a checkbox");
else alert("Please check a checkbox");
}
If you have a question about the code, just comment.
I use l=checkboxs.length to improve the performance. See http://www.erichynds.com/javascript/javascript-loop-performance-caching-the-length-property-of-an-array/

I would opt for a more functional approach. Since ES6 we have been given such nice tools to solve our problems, so why not use them.
Let's begin with giving the checkboxes a class so we can round them up very nicely.
I prefer to use a class instead of input[type="checkbox"] because now the solution is more generic and can be used also when you have more groups of checkboxes in your document.
HTML
<input type="checkbox" class="checkbox" value=ck1 /> ck1<br />
<input type="checkbox" class="checkbox" value=ck2 /> ck2<br />
JavaScript
function atLeastOneCheckboxIsChecked(){
const checkboxes = Array.from(document.querySelectorAll(".checkbox"));
return checkboxes.reduce((acc, curr) => acc || curr.checked, false);
}
When called, the function will return false if no checkbox has been checked and true if one or both is.
It works as follows, the reducer function has two arguments, the accumulator (acc) and the current value (curr). For every iteration over the array, the reducer will return true if either the accumulator or the current value is true.
the return value of the previous iteration is the accumulator of the current iteration, therefore, if it ever is true, it will stay true until the end.

Check this.
You can't access form inputs via their name. Use document.getElements methods instead.

Vanilla JS:
var checkboxes = document.getElementsByClassName('activityCheckbox'); // puts all your checkboxes in a variable
function activitiesReset() {
var checkboxesChecked = function () { // if a checkbox is checked, function ends and returns true. If all checkboxes have been iterated through (which means they are all unchecked), returns false.
for (var i = 0; i < checkboxes.length; i++) {
if (checkboxes[i].checked) {
return true;
}
}
return false;
}
error[2].style.display = 'none'; // an array item specific to my project - it's a red label which says 'Please check a checkbox!'. Here its display is set to none, so the initial non-error label is visible instead.
if (submitCounter > 0 && checkboxesChecked() === false) { // if a form submit has been attempted, and if all checkboxes are unchecked
error[2].style.display = 'block'; // red error label is now visible.
}
}
for (var i=0; i<checkboxes.length; i++) { // whenever a checkbox is checked or unchecked, activitiesReset runs.
checkboxes[i].addEventListener('change', activitiesReset);
}
Explanation:
Once a form submit has been attempted, this will update your checkbox section's label to notify the user to check a checkbox if he/she hasn't yet. If no checkboxes are checked, a hidden 'error' label is revealed prompting the user to 'Please check a checkbox!'. If the user checks at least one checkbox, the red label is instantaneously hidden again, revealing the original label. If the user again un-checks all checkboxes, the red label returns in real-time. This is made possible by JavaScript's onchange event (written as .addEventListener('change', function(){});

You can check that atleast one checkbox is checked or not using this simple code. You can also drop your message.
Reference Link
<label class="control-label col-sm-4">Check Box 2</label>
<input type="checkbox" name="checkbox2" id="checkbox2" value=ck1 /> ck1<br />
<input type="checkbox" name="checkbox2" id="checkbox2" value=ck2 /> ck2<br />
<script>
function checkFormData() {
if (!$('input[name=checkbox2]:checked').length > 0) {
document.getElementById("errMessage").innerHTML = "Check Box 2 can not be null";
return false;
}
alert("Success");
return true;
}
</script>

< script type = "text/javascript" src = "js/jquery-1.6.4.min.js" > < / script >
< script type = "text/javascript" >
function checkSelectedAtleastOne(clsName) {
if (selectedValue == "select")
return false;
var i = 0;
$("." + clsName).each(function () {
if ($(this).is(':checked')) {
i = 1;
}
});
if (i == 0) {
alert("Please select atleast one users");
return false;
} else if (i == 1) {
return true;
}
return true;
}
$(document).ready(function () {
$('#chkSearchAll').click(function () {
var checked = $(this).is(':checked');
$('.clsChkSearch').each(function () {
var checkBox = $(this);
if (checked) {
checkBox.prop('checked', true);
} else {
checkBox.prop('checked', false);
}
});
});
//for select and deselect 'select all' check box when clicking individual check boxes
$(".clsChkSearch").click(function () {
var i = 0;
$(".clsChkSearch").each(function () {
if ($(this).is(':checked')) {}
else {
i = 1; //unchecked
}
});
if (i == 0) {
$("#chkSearchAll").attr("checked", true)
} else if (i == 1) {
$("#chkSearchAll").attr("checked", false)
}
});
});
< / script >

Prevent user from deselecting last checked checkbox.
jQuery (original answer).
$('input[type="checkbox"][name="chkBx"]').on('change',function(){
var getArrVal = $('input[type="checkbox"][name="chkBx"]:checked').map(function(){
return this.value;
}).toArray();
if(getArrVal.length){
//execute the code
$('#msg').html(getArrVal.toString());
} else {
$(this).prop("checked",true);
$('#msg').html("At least one value must be checked!");
return false;
}
});
UPDATED ANSWER 2019-05-31
Plain JS
let i,
el = document.querySelectorAll('input[type="checkbox"][name="chkBx"]'),
msg = document.getElementById('msg'),
onChange = function(ev){
ev.preventDefault();
let _this = this,
arrVal = Array.prototype.slice.call(
document.querySelectorAll('input[type="checkbox"][name="chkBx"]:checked'))
.map(function(cur){return cur.value});
if(arrVal.length){
msg.innerHTML = JSON.stringify(arrVal);
} else {
_this.checked=true;
msg.innerHTML = "At least one value must be checked!";
}
};
for(i=el.length;i--;){el[i].addEventListener('change',onChange,false);}
<label><input type="checkbox" name="chkBx" value="value1" checked> Value1</label>
<label><input type="checkbox" name="chkBx" value="value2"> Value2</label>
<label><input type="checkbox" name="chkBx" value="value3"> Value3</label>
<div id="msg"></div>

$('input:checkbox[type=checkbox]').on('change',function(){
if($('input:checkbox[type=checkbox]').is(":checked") == true){
$('.removedisable').removeClass('disabled');
}else{
$('.removedisable').addClass('disabled');
});

if(($("#checkboxid1").is(":checked")) || ($("#checkboxid2").is(":checked"))
|| ($("#checkboxid3").is(":checked"))) {
//Your Code here
}
You can use this code to verify that checkbox is checked at least one.
Thanks!!

Javascript Validating in a loop

I have two radio buttons on the top (YES/NO) If yes the javascript function showhideform shows another text box(certificate). This form is in a loop as you see with all my outputs.If yes is chosen and loop is 1 everything works fine onsubmit. If Yes and I submit when loop is 2 it only validates certificate textbox 2 and forgets about certificate textbox 1. I need it to validate both if yes is chosen twice.
Radio Buttons:
<input
type="radio"
value="No"
name="abc_<cfoutput>#BAdd#</cfoutput>"
id="noabc_<cfoutput>#BAdd#</cfoutput>"
onchange="showhideForm_<cfoutput>#BAdd#</cfoutput>(this.value);"/>
<label for="noabc_<cfoutput>#BAdd#</cfoutput>">No</label>
<input
type="radio"
value="Yes"
name="abc_<cfoutput>#BAdd#</cfoutput>"
id="abc_<cfoutput>#BAdd#</cfoutput>"
required="yes"
onchange="showhideForm_<cfoutput>#BAdd#</cfoutput>(this.value);"/>
<label for="abc_<cfoutput>#BAdd#</cfoutput>">Yes</label>
Show / Hide Radio Buttons:
function showhideForm_<cfoutput>#BAdd#</cfoutput>(abc_<cfoutput>#BAdd#</cfoutput>) {
if (abc_<cfoutput>#BAdd#</cfoutput> == "Yes") {
document.getElementById("div1_<cfoutput>#BAdd#</cfoutput>").style.display = 'block';
document.getElementById("div2_<cfoutput>#BAdd#</cfoutput>").style.display = 'none';
}
else if (abc_<cfoutput>#BAdd#</cfoutput> == "No") {
document.getElementById("div2_<cfoutput>#BAdd#</cfoutput>").style.display = 'block';
document.getElementById("div1_<cfoutput>#BAdd#</cfoutput>").style.display = 'none';
}
}
Validating through loop:
function doSubmit(n) {
var QnoText = ['abc_<cfoutput>#BAdd#</cfoutput>']; // add IDs here for questions with optional text input
var ids = '';
flag = true;
for (i=0; i<QnoText.length; i++) {
CkStatus = document.getElementById(QnoText[i]).checked;
ids = QnoText[i]+'Certificate_<cfoutput>#BAdd#</cfoutput>' + n;
if (CkStatus && document.getElementById(ids).value == '') {
alert('Please enter certificate number ' + n + '.');
document.getElementById(ids).focus();
flag = false;
}
}
return flag;
}
Certificate textbox:
<input
type="text"
name="abc_<cfoutput>#BAdd#</cfoutput>Certificate_<cfoutput>#BAdd#</cfoutput>"
validateat="onSubmit"
validate="maxlength"
id="abc_<cfoutput>#BAdd#</cfoutput>Certificate_<cfoutput>#BAdd#</cfoutput>"
size="54"
maxlength="120"
value="">
submit button:
//return doSubmit(1);

It looks like the n is just a numbering/index to the id of the input textbox it is validating.
Looking at your code, CKStatus seems to me is a checkbox. If it is checked, it will validate the certificate input text box according to the parameter n.

After days of working on it I have finally figured it out!! I just wanted to say thanks to everyone that has helped and this is the code for anyone who was interested!
<script type="text/javascript">
function doSubmit() {
var count =<cfoutput>#BAdd#</cfoutput>;
flag = true;
for (i=1; i<=count; i++){
var ids = 'abc_'+i +'Certificate_'+i;
var Radio = 'abc_'+i
CkStatus = document.getElementById(Radio).checked;
if (CkStatus && document.getElementById(ids).value == '') {
alert('Please enter certificate number ' +i);
document.getElementById(ids).focus();
flag = false;
}
}
return flag;
}
</script>

Validating a single radio button is not working in available javascript validation script

I have randomly generated radio button series like
<input type="radio" name="creatorusers" value="1">
<input type="radio" name="creatorusers" value="1">
<input type="radio" name="creatorusers" value="1">
<input type="radio" name="creatorusers" value="1">
.....so on
But I get only ONE radio button and execute the javascript validation given for it to chk whether the radio button is selected or not, then it doesnt work
Ples help me out in resolving this.
mycreator = -1;
for (i=frm.creatorusers.length-1; i > -1; i--) {
if (frm.creatorusers[i].checked) {
mycreator = i; i = -1;
}
}
if (mycreator == -1) {
alert("You must select a Creator User!");
return false;
}

Always (!) use the var keyword. Otherwise your variables will be in the global scope (yes, even those in function bodies), which can make for some bugs that are hard to track down.
As #Felix pointed out, creatorusers will only be an array if there is more than one element with that name in the form. You can create a single-element array when necessary to work around that.
Here is an abstracted function that can validate an arbitrary checkbox list.
function ensureChecked(checkboxes, error) {
if (checkboxes) {
var cbx = (checkboxes.length > 0) ? checkboxes : [checkboxes];
for (var i=0; i<cbx.length; i++) {
if (cbx[i].checked) {
return true;
}
}
alert(error);
}
return false;
}
call as
ensureChecked(frm.creatorusers, "You must select a Creator User!");

Ah now I got. If you only have one radio button, then frm.creatorusers is not an array. Just skip it:
var mycreator = -1;
var checked = false;
if(typeof frm.creatorusers.length === 'number') {
for (var i=frm.creatorusers.length; i--; ) {
if (frm.creatorusers[i].checked) {
mycreator = i;
checked = true;
break;
}
}
}
else if(frm.creatorusers.checked){
mycreator = //? what here?
checked = true;
}
if(!checked) {
alert("You must select a Creator User!");
return false;
}
If mycreator was just for checking whether a button was selected or not, you can completely remove it from the code above.
Some further notes to your code:
Always declare variables with var, otherwise they will be global.
Use break to end a loop.
Maybe it is just because of copy and paste, but having a lot of radio buttons with the same value does not make much sense.

You can do something like this:
function validate(frm){
var isChecked = false;
for (var i=0; i<frm.elements.length; i++)
{
if (frm.elements[i].type === 'radio'){
if (frm.elements[i].checked === true){
isChecked = true;
break;
}
}
}
if (isChecked === true){
return true;
}
else{
alert('You should select an option first !');
}
}
Now you should call above function on onsubmit event of the form:
<form onsubmit="return validate(this);">
Now the validate function will make sure that at least one radio button is checked otherwise it won't submit.

this should do it
function isRadioSelected(btn) {
if(typeof btn.length === 'number') {
for(var i=0;i<btn.length;i++)
if(btn[i].checked) return true
}else{
if(btn.checked) return true
}
return false
}

You could try something like this instead:
<html>
<head>
<script type="text/javascript">
function confirmsubmit() {
var btn = document.formname.buttonname
if (btn.checked == false)
{
window.alert("You did not click the button.");
btn.focus();
return false;
}
return true;
}
</script>
</head>
<body>
<form method="post" action="mailto:youremail#yourdomain.com"
name="formname" onsubmit="return confirmsubmit();">
click here: <input type="radio" name="buttonname"><br />
<p><input type="submit" value="Submit" name="submit"></p>
</form>
</body>
</html>