Develop Reference

form submit with checkboxes [duplicate]

I've got a load of checkboxes that are checked by default. My users will probably uncheck a few (if any) of the checkboxes and leave the rest checked.
Is there any way to make the form POST the checkboxes that are not checked, rather than the ones that are checked?

The solution I liked the most so far is to put a hidden input with the same name as the checkbox that might not be checked. I think it works so that if the checkbox isn't checked, the hidden input is still successful and sent to the server but if the checkbox is checked it will override the hidden input before it. This way you don't have to keep track of which values in the posted data were expected to come from checkboxes.
<form>
<input type='hidden' value='0' name='selfdestruct'>
<input type='checkbox' value='1' name='selfdestruct'>
</form>

Add a hidden input for the checkbox with a different ID:
<input id='testName' type='checkbox' value='Yes' name='testName'>
<input id='testNameHidden' type='hidden' value='No' name='testName'>
Before submitting the form, disable the hidden input based on the checked condition:
form.addEventListener('submit', () => {
if(document.getElementById("testName").checked) {
document.getElementById('testNameHidden').disabled = true;
}
}

I solved it by using vanilla JavaScript:
<input type="hidden" name="checkboxName" value="0"><input type="checkbox" onclick="this.previousSibling.value=1-this.previousSibling.value">
Be careful not to have any spaces or linebreaks between this two input elements!
You can use this.previousSibling.previousSibling to get "upper" elements.
With PHP you can check the named hidden field for 0 (not set) or 1 (set).

My personal favorite is to add a hidden field with the same name that will be used if the check-box is unchecked. But the solution is not as easy as it may seems.
If you add this code:
<form>
<input type='hidden' value='0' name='selfdestruct'>
<input type='checkbox' value='1' name='selfdestruct'>
</form>
The browser will not really care about what you do here. The browser will send both parameters to the server, and the server has to decide what to do with them.
PHP for example takes the last value as the one to use (see: Authoritative position of duplicate HTTP GET query keys)
But other systems I worked with (based on Java) do it the way around - they offer you only the first value.
.NET instead will give you an array with both elements instead
I'll try to test this with node.js, Python and Perl at sometime.

you don't need to create a hidden field for all checkboxes just copy my code.
it will change the value of checkbox if not checked the value will assign 0 and if checkbox checked then assign value into 1
$("form").submit(function () {
var this_master = $(this);
this_master.find('input[type="checkbox"]').each( function () {
var checkbox_this = $(this);
if( checkbox_this.is(":checked") == true ) {
checkbox_this.attr('value','1');
} else {
checkbox_this.prop('checked',true);
//DONT' ITS JUST CHECK THE CHECKBOX TO SUBMIT FORM DATA
checkbox_this.attr('value','0');
}
})
})

A common technique around this is to carry a hidden variable along with each checkbox.
<input type="checkbox" name="mycheckbox" />
<input type="hidden" name="mycheckbox.hidden"/>
On the server side, we first detect list of hidden variables and for each of the hidden variable, we try to see if the corresponding checkbox entry is submitted in the form data or not.
The server side algorithm would probably look like:
for input in form data such that input.name endswith .hidden
checkboxName = input.name.rstrip('.hidden')
if chceckbName is not in form, user has unchecked this checkbox
The above doesn't exactly answer the question, but provides an alternate means of achieving similar functionality.

I know this question is 3 years old but I found a solution that I think works pretty well.
You can do a check if the $_POST variable is assigned and save it in a variable.
$value = isset($_POST['checkboxname'] ? 'YES' : 'NO';
the isset() function checks if the $_POST variable is assigned. By logic if it is not assigned then the checkbox is not checked.

$('input[type=checkbox]').on("change",function(){
var target = $(this).parent().find('input[type=hidden]').val();
if(target == 0)
{
target = 1;
}
else
{
target = 0;
}
$(this).parent().find('input[type=hidden]').val(target);
});
<p>
<input type="checkbox" />
<input type="hidden" name="test_checkbox[]" value="0" />
</p>
<p>
<input type="checkbox" />
<input type="hidden" name="test_checkbox[]" value="0" />
</p>
<p>
<input type="checkbox" />
<input type="hidden" name="test_checkbox[]" value="0" />
</p>
If you leave out the name of the checkbox it doesn't get passed.
Only the test_checkbox array.

You can do some Javascript in the form's submit event. That's all you can do though, there's no way to get browsers to do this by themselves. It also means your form will break for users without Javascript.
Better is to know on the server which checkboxes there are, so you can deduce that those absent from the posted form values ($_POST in PHP) are unchecked.

I also like the solution that you just post an extra input field, using JavaScript seems a little hacky to me.
Depending on what you use for you backend will depend on which input goes first.
For a server backend where the first occurrence is used (JSP) you should do the following.
<input type="checkbox" value="1" name="checkbox_1"/>
<input type="hidden" value="0" name="checkbox_1"/>
For a server backend where the last occurrence is used (PHP,Rails) you should do the following.
<input type="hidden" value="0" name="checkbox_1"/>
<input type="checkbox" value="1" name="checkbox_1"/>
For a server backend where all occurrences are stored in a list data type ([],array). (Python / Zope)
You can post in which ever order you like, you just need to try to get the value from the input with the checkbox type attribute. So the first index of the list if the checkbox was before the hidden element and the last index if the checkbox was after the hidden element.
For a server backend where all occurrences are concatenated with a comma (ASP.NET / IIS)
You will need to (split/explode) the string by using a comma as a delimiter to create a list data type. ([])
Now you can attempt to grab the first index of the list if the checkbox was before the hidden element and grab the last index if the checkbox was after the hidden element.
image source

I would actually do the following.
Have my hidden input field with the same name with the checkbox input
<input type="hidden" name="checkbox_name[]" value="0" />
<input type="checkbox" name="checkbox_name[]" value="1" />
and then when i post I first of all remove the duplicate values picked up in the $_POST array, atfer that display each of the unique values.
$posted = array_unique($_POST['checkbox_name']);
foreach($posted as $value){
print $value;
}
I got this from a post remove duplicate values from array

"I've gone with the server approach. Seems to work fine - thanks. – reach4thelasers Dec 1 '09 at 15:19" I would like to recommend it from the owner. As quoted: javascript solution depends on how the server handler (I didn't check it)
such as
if(!isset($_POST["checkbox"]) or empty($_POST["checkbox"])) $_POST["checkbox"]="something";

Most of the answers here require the use of JavaScript or duplicate input controls. Sometimes this needs to be handled entirely on the server-side.
I believe the (intended) key to solving this common problem is the form's submission input control.
To interpret and handle unchecked values for checkboxes successfully you need to have knowledge of the following:
The names of the checkboxes
The name of the form's submission input element
By checking whether the form was submitted (a value is assigned to the submission input element), any unchecked checkbox values can be assumed.
For example:
<form name="form" method="post">
<input name="value1" type="checkbox" value="1">Checkbox One<br/>
<input name="value2" type="checkbox" value="1" checked="checked">Checkbox Two<br/>
<input name="value3" type="checkbox" value="1">Checkbox Three<br/>
<input name="submit" type="submit" value="Submit">
</form>
When using PHP, it's fairly trivial to detect which checkboxes were ticked.
<?php
$checkboxNames = array('value1', 'value2', 'value3');
// Persisted (previous) checkbox state may be loaded
// from storage, such as the user's session or a database.
$checkboxesThatAreChecked = array();
// Only process if the form was actually submitted.
// This provides an opportunity to update the user's
// session data, or to persist the new state of the data.
if (!empty($_POST['submit'])) {
foreach ($checkboxNames as $checkboxName) {
if (!empty($_POST[$checkboxName])) {
$checkboxesThatAreChecked[] = $checkboxName;
}
}
// The new state of the checkboxes can be persisted
// in session or database by inspecting the values
// in $checkboxesThatAreChecked.
print_r($checkboxesThatAreChecked);
}
?>
Initial data could be loaded on each page load, but should be only modified if the form was submitted. Since the names of the checkboxes are known beforehand, they can be traversed and inspected individually, so that the the absence of their individual values indicates that they are not checked.

I've tried Sam's version first.
Good idea, but it causes there to be multiple elements in the form with the same name. If you use any javascript that finds elements based on name, it will now return an array of elements.
I've worked out Shailesh's idea in PHP, it works for me.
Here's my code:
/* Delete '.hidden' fields if the original is present, use '.hidden' value if not. */
foreach ($_POST['frmmain'] as $field_name => $value)
{
// Only look at elements ending with '.hidden'
if ( !substr($field_name, -strlen('.hidden')) ) {
break;
}
// get the name without '.hidden'
$real_name = substr($key, strlen($field_name) - strlen('.hidden'));
// Create a 'fake' original field with the value in '.hidden' if an original does not exist
if ( !array_key_exists( $real_name, $POST_copy ) ) {
$_POST[$real_name] = $value;
}
// Delete the '.hidden' element
unset($_POST[$field_name]);
}

You can also intercept the form.submit event and reverse check before submit
$('form').submit(function(event){
$('input[type=checkbox]').prop('checked', function(index, value){
return !value;
});
});

I use this block of jQuery, which will add a hidden input at submit-time to every unchecked checkbox. It will guarantee you always get a value submitted for every checkbox, every time, without cluttering up your markup and risking forgetting to do it on a checkbox you add later. It's also agnostic to whatever backend stack (PHP, Ruby, etc.) you're using.
// Add an event listener on #form's submit action...
$("#form").submit(
function() {
// For each unchecked checkbox on the form...
$(this).find($("input:checkbox:not(:checked)")).each(
// Create a hidden field with the same name as the checkbox and a value of 0
// You could just as easily use "off", "false", or whatever you want to get
// when the checkbox is empty.
function(index) {
var input = $('<input />');
input.attr('type', 'hidden');
input.attr('name', $(this).attr("name")); // Same name as the checkbox
input.attr('value', "0"); // or 'off', 'false', 'no', whatever
// append it to the form the checkbox is in just as it's being submitted
var form = $(this)[0].form;
$(form).append(input);
} // end function inside each()
); // end each() argument list
return true; // Don't abort the form submit
} // end function inside submit()
); // end submit() argument list

$('form').submit(function () {
$(this).find('input[type="checkbox"]').each( function () {
var checkbox = $(this);
if( checkbox.is(':checked')) {
checkbox.attr('value','1');
} else {
checkbox.after().append(checkbox.clone().attr({type:'hidden', value:0}));
checkbox.prop('disabled', true);
}
})
});

I see this question is old and has so many answers, but I'll give my penny anyway.
My vote is for the javascript solution on the form's 'submit' event, as some has pointed out. No doubling the inputs (especially if you have long names and attributes with php code mixed with html), no server side bother (that would require to know all field names and to check them down one by one), just fetch all the unchecked items, assign them a 0 value (or whatever you need to indicate a 'not checked' status) and then change their attribute 'checked' to true
$('form').submit(function(e){
var b = $("input:checkbox:not(:checked)");
$(b).each(function () {
$(this).val(0); //Set whatever value you need for 'not checked'
$(this).attr("checked", true);
});
return true;
});
this way you will have a $_POST array like this:
Array
(
[field1] => 1
[field2] => 0
)

What I did was a bit different. First I changed the values of all the unchecked checkboxes. To "0", then selected them all, so the value would be submitted.
function checkboxvalues(){
$("#checkbox-container input:checkbox").each(function({
if($(this).prop("checked")!=true){
$(this).val("0");
$(this).prop("checked", true);
}
});
}

I would prefer collate the $_POST
if (!$_POST['checkboxname']) !$_POST['checkboxname'] = 0;
it minds, if the POST doesn't have have the 'checkboxname'value, it was unckecked so, asign a value.
you can create an array of your ckeckbox values and create a function that check if values exist, if doesn`t, it minds that are unchecked and you can asign a value

Might look silly, but it works for me. The main drawback is that visually is a radio button, not a checkbox, but it work without any javascript.
HTML
Initialy checked
<span><!-- set the check attribute for the one that represents the initial value-->
<input type="radio" name="a" value="1" checked>
<input type="radio" name="a" value="0">
</span>
<br/>
Initialy unchecked
<span><!-- set the check attribute for the one that represents the initial value-->
<input type="radio" name="b" value="1">
<input type="radio" name="b" value="0" checked>
</span>
and CSS
span input
{position: absolute; opacity: 0.99}
span input:checked
{z-index: -10;}
span input[value="0"]
{opacity: 0;}
fiddle here
I'd like to hear any problems you find with this code, cause I use it in production

The easiest solution is a "dummy" checkbox plus hidden input if you are using jquery:
<input id="id" type="hidden" name="name" value="1/0">
<input onchange="$('#id').val(this.checked?1:0)" type="checkbox" id="dummy-id"
name="dummy-name" value="1/0" checked="checked/blank">
Set the value to the current 1/0 value to start with for BOTH inputs, and checked=checked if 1. The input field (active) will now always be posted as 1 or 0. Also the checkbox can be clicked more than once before submission and still work correctly.

Example on Ajax actions is(':checked') used jQuery instead of .val();
var params = {
books: $('input#users').is(':checked'),
news : $('input#news').is(':checked'),
magazine : $('input#magazine').is(':checked')
};
params will get value in TRUE OR FALSE..

Checkboxes usually represent binary data that are stored in database as Yes/No, Y/N or 1/0 values. HTML checkboxes do have bad nature to send value to server only if checkbox is checked! That means that server script on other site must know in advance what are all possible checkboxes on web page in order to be able to store positive (checked) or negative (unchecked) values. Actually only negative values are problem (when user unchecks previously (pre)checked value - how can server know this when nothing is sent if it does not know in advance that this name should be sent). If you have a server side script which dynamically creates UPDATE script there's a problem because you don't know what all checkboxes should be received in order to set Y value for checked and N value for unchecked (not received) ones.
Since I store values 'Y' and 'N' in my database and represent them via checked and unchecked checkboxes on page, I added hidden field for each value (checkbox) with 'Y' and 'N' values then use checkboxes just for visual representation, and use simple JavaScript function check() to set value of if according to selection.
<input type="hidden" id="N1" name="N1" value="Y" />
<input type="checkbox"<?php if($N1==='Y') echo ' checked="checked"'; ?> onclick="check(this);" />
<label for="N1">Checkbox #1</label>
use one JavaScript onclick listener and call function check() for each checkboxe on my web page:
function check(me)
{
if(me.checked)
{
me.previousSibling.previousSibling.value='Y';
}
else
{
me.previousSibling.previousSibling.value='N';
}
}
This way 'Y' or 'N' values are always sent to server side script, it knows what are fields that should be updated and there's no need for conversion of checbox "on" value into 'Y' or not received checkbox into 'N'.
NOTE: white space or new line is also a sibling so here I need .previousSibling.previousSibling.value. If there's no space between then only .previousSibling.value
You don't need to explicitly add onclick listener like before, you can use jQuery library to dynamically add click listener with function to change value to all checkboxes in your page:
$('input[type=checkbox]').click(function()
{
if(this.checked)
{
$(this).prev().val('Y');
}
else
{
$(this).prev().val('N');
}
});

#cpburnz got it right but to much code, here is the same idea using less code:
JS:
// jQuery OnLoad
$(function(){
// Listen to input type checkbox on change event
$("input[type=checkbox]").change(function(){
$(this).parent().find('input[type=hidden]').val((this.checked)?1:0);
});
});
HTML (note the field name using an array name):
<div>
<input type="checkbox" checked="checked">
<input type="hidden" name="field_name[34]" value="1"/>
</div>
<div>
<input type="checkbox">
<input type="hidden" name="field_name[35]" value="0"/>
</div>
<div>
And for PHP:
<div>
<input type="checkbox"<?=($boolean)?' checked="checked"':''?>>
<input type="hidden" name="field_name[<?=$item_id?>]" value="<?=($boolean)?1:0?>"/>
</div>

All answers are great, but if you have multiple checkboxes in a form with the same name and you want to post the status of each checkbox. Then i have solved this problem by placing a hidden field with the checkbox (name related to what i want).
<input type="hidden" class="checkbox_handler" name="is_admin[]" value="0" />
<input type="checkbox" name="is_admin_ck[]" value="1" />
then control the change status of checkbox by below jquery code:
$(documen).on("change", "input[type='checkbox']", function() {
var checkbox_val = ( this.checked ) ? 1 : 0;
$(this).siblings('input.checkbox_handler').val(checkbox_val);
});
now on change of any checkbox, it will change the value of related hidden field. And on server you can look only to hidden fields instead of checkboxes.
Hope this will help someone have this type of problem. cheer :)

You can add hidden elements before submitting form.
$('form').submit(function() {
$(this).find('input[type=checkbox]').each(function (i, el) {
if(!el.checked) {
var hidden_el = $(el).clone();
hidden_el[0].checked = true;
hidden_el[0].value = '0';
hidden_el[0].type = 'hidden'
hidden_el.insertAfter($(el));
}
})
});

The problem with checkboxes is that if they are not checked then they are not posted with your form. If you check a checkbox and post a form you will get the value of the checkbox in the $_POST variable which you can use to process a form, if it's unchecked no value will be added to the $_POST variable.
In PHP you would normally get around this problem by doing an isset() check on your checkbox element. If the element you are expecting isn't set in the $_POST variable then we know that the checkbox is not checked and the value can be false.
if(!isset($_POST['checkbox1']))
{
$checkboxValue = false;
} else {
$checkboxValue = $_POST['checkbox1'];
}
But if you have created a dynamic form then you won't always know the name attribute of your checkboxes, if you don't know the name of the checkbox then you can't use the isset function to check if this has been sent with the $_POST variable.

function SubmitCheckBox(obj) {
obj.value = obj.checked ? "on" : "off";
obj.checked = true;
return obj.form.submit();
}
<input type=checkbox name="foo" onChange="return SubmitCheckBox(this);">

If you want to submit an array of checkbox values (including un-checked items) then you could try something like this:
<form>
<input type="hidden" value="0" name="your_checkbox_array[]"><input type="checkbox">Dog
<input type="hidden" value="0" name="your_checkbox_array[]"><input type="checkbox">Cat
</form>
$('form').submit(function(){
$('input[type="checkbox"]:checked').prev().val(1);
});

Learning Javascript: adding 2 numbers

I am learning javascript and trying to complete a simple excercise: add 2 numbers that are entered in 2 separate entry field and show the sum on a page. The script below is executed when you press a button. The problem I'm somehow unable to solve is that the result of the addition is always zero. What I am doing wrong here?
var inputA = document.getElementById("numberA");
var convertA = +inputA;
var inputB = document.getElementById("numberB");
var convertB = +inputB;
function myFunction() {
document.getElementById("result").innerHTML = convertA + convertB;
}

You need to take the value of the text input .
var inputA = document.getElementById("numberA").value;
// ^^^^^^
Please move the variables inside into the function, because the value property returns a string and not a referece to the object.
function myFunction() {
var inputA = document.getElementById("numberA").value;
var inputB = document.getElementById("numberB").value;
var convertA = +inputA;
var convertB = +inputB;
document.getElementById("result").innerHTML = convertA + convertB;
}
<input id="numberA" type="text">
<input id="numberB" type="text">
<button onclick="myFunction()">calc</button>
<div id="result"></div>

One example of this is to grab the values and then parse them into Integers before adding them together. Setting a value of 0 on the input prevents the user from getting a result of NaN. You could also remove these initial values and write an if statement to check for empty values.
Anyway here is what I came up with:
<!DOCTYPE html>
<html>
<head>
<title>Test Function</title>
</head>
<body>
<!-- Create Inputs -->
<input id="numberA" type="number" value="0">
<input id="numberB" type="number" value="0">
<!-- Function Button -->
<button onclick="myFunction()">Add Numbers</button>
<!-- Display Result -->
<div id="result"></div>
<!-- Run Script -->
<script>
// Get Inputs by ID
var inputA = document.getElementById("numberA");
var inputB = document.getElementById("numberB");
// Parse Values and Add Integers
function myFunction() {
document.getElementById("result").innerHTML = parseInt(inputA.value) + parseInt(inputB.value);
}
</script>
</body>
</html>

before start coding on Javascript I think that you must be aware about how it interacts with elements in page: every single element, is represented by DOM (Domain Object Model) and Javascript can interact with elements querying this DOM for obtain them, but in the form of their virtual representation: a DOM Object.
That's what your trying to sum... two DOM objects that represents the input elements.
As objects, they have their own properties accessible by the dot sign, and for get the values of those fields, the answer of #Nina Scholz is the way.
So, when you get the element by Id, or elements by tag, by name etc, etc... you have to consider this.

Although not related. Base on Nina Scholz answer, You must take consider the type of input and change it to number so you will not end up with undefined or NaN result.

Converting text to lowercase/uppercase with a pending a radio button

I am writing a Javascript program that takes a users input text, then (pending a radio button check – lowerCase/UpperCase) converts the input text to either lowercase/upperCase and outputs the value back to the form.
Purely trying to learn on my own Javascript. I am moderately new (but savvy) to JS. Pretty solid on HTML, CSS, Java, but BRAND new with interacting with page elements.
I have dug around for two days to try and solve this. I have even checked out a few books at my local library. (Currently reading the text, Microsoft guide to CSS/HTML, and JS). What other books would you recommend in order to under JS more?
Here is the code below. Although I know one can use CSS in order to convert this and I have done this. I'm purely just wanting to figure out Javascript.
<!DOCTYPE html>
<html>
<head>
<title> Case Changer By: Elliot Granet</title>
<style>
function convert(){
var convertedText = document.test.input.value;
if(document.getElementById("lowerCase").checked = true){
var output = convertedText.toLowerCase();
}else {
output = convertedText.toUpperCase();
}
document.getElementById('outputText').value = output;
}
convert();
</head>
The rest -
<body>
<h3>Choose your Conversion method below:</h3>
<form action="getElementById">
<fieldset>
<input id="lowerCase" type="radio" name="case" value="lowerCase">Lower Case<br>
<input id ="upperCase" type="radio" name="case" value="upperCase">Upper Case<br><br>
</fieldset>
<fieldset>
<textarea id="inputText" name="input" form="inputText">Enter text here to be Converted...</textarea>
</fieldset><br>
<fieldset>
<textarea id ="outputText" name="output" form="outputText">Converted text will appear here...</textarea>
</fieldset>
<input type="button" value="Convert">
</form>
</body>
</html>

You need to make few changes to make this function work.
style is an invalid tag to put js code. You need to put it inside <script> tag
If you are writing this function inside header yo may come across error since before DOM is ready it will try to get value of textarea with id inputText.
document.getElementById(idName').value but not is right syntax to get the value of element using id
Attaching convert() with the button. So when you will click on button the function will execute.
5.document.getElementById("lowerCase").checked = true this is wrong.It mean that checkbox will get checked as = will assign the value . Instead you need to compare the value. So use == or ===
if you declare var output inside if loop it wont be available inside else. So you need to declare it outside the if-else loop
Hope this snippet will be useful
HTML
<input type="button" value="Convert" onclick="convert()">
JS
window.load =convert; // convert function will be called after window is ready
function convert(){
var output; //variable declaration outside if-else loop
var convertedText = document.getElementById('inputText').value; //document.getElementById
if(document.getElementById("lowerCase").checked == true){ // == comparision
output = convertedText.toLowerCase();
}
else {
output = convertedText.toUpperCase();
}
document.getElementById('outputText').value = output;
}
EXAMPLE

Create unique name for <input> in form

Okay, first thing, I had a lot of trouble thinking of a title for this, and also of what to search for in Google. So that may just be me being stupid, but here is what I would like you help with.
I have a form, that has a button that will add additional input fields, but I would like the the name of the field to iterate everytime the button is pressed. E.g. the first time it will be:
<input type="textfield" name="field1" value=""/>
Then the second time it is pressed, it will be:
<input type="textfield" name="field2" value=""/>
I also have a small example of what I currently have here: http://jsfiddle.net/5gh75/14/
Please let me know if you can help me, or if you require more info thanks :)

The best way to handle this is to name them all field[].
When handled by the server-side code, it will build an array for you. For instance, in PHP you would get $_POST['field'][0], $_POST['field'][1] and so on.

For your example:
JQuery
var i=0;
$('span.add').click(function () {
$('<input>').attr({
type: 'textfield',
name: 'program'+i
}).appendTo('#addsoftware');
i++;
});
JSFiddle.
But #Kolink-s answer is much better.

Edit: I just saw the previous posts after sending this. Using an array would definitely be better, and JQuery is always nice :).
Just use some javascript:
<HTML>
<HEAD>
<TITLE>Dynamically add Textbox, Radio, Button in html Form using JavaScript</TITLE>
<SCRIPT language="javascript">
idx = 0;
function add() {
//Create an input type dynamically.
var element = document.createElement("input");
//Assign different attributes to the element.
element.setAttribute("type", "textfield");
element.setAttribute("name", "field" . idx);
element.setAttribute("value", "");
idx++;
var foo = document.getElementById("fooBar");
//Append the element in page (in span).
foo.appendChild(element);
}
</SCRIPT>
</HEAD>
<BODY>
<FORM>
<H2>Dynamically add element in form.</H2>
Select the element and hit Add to add it in form.
<BR/>
<INPUT type="button" value="Add" onclick="add()"/>
<span id="fooBar"> </span>
</FORM>
</BODY>
</HTML>
I took this example from: Add more text fields dynamically in new line (html)

Get textbox value in Javascript (single/multiple fields)

I have a field in my page named as "myField"
Now this is dynamic So there are 2 cases i.e. it can be just 1 field as;
<input type="text" name="myField" />
OR there can be 2 fields as below;
<input type="text" name="myField" />
<input type="hidden" name="myField" />
I use the following code to access the value in JS;
document.forms[0].myField[0].value
However, this does not work if there is only 1 field (as in the first case)
How do I write dynamic JS code to handle the same?
It should be cross browser compatible.

Yes, because in the first case you should use document.forms[0].myField.value.
I'd suggest to retrieve elements with getElementsByName() method:
var val = document.getElementsByName("myField")[0].value;

better way is to give a unique ID to each element and then get it with
document.getElementById(id).value

Have a look at JQuery, and here's some information on how to get the value out.

provided there is at least one element name "myField"
var count = document.forms[0].myField.length;
for(var i=0; i < count; i++){
// do something with document.forms[0].myField[i].value
console.log(document.forms[0].myField[i].value);
}
fiddle : http://jsfiddle.net/HtrrT/