skip to Main Content

I need to “invert” a checkbox, i.e. submit the value if the checkbox is unchecked, and leave it empty if the checkbox is checked.

I do not want to prevent form submission!

I can think of two approaches:

  1. change appearance of the checkbox so that it looks checked if it actually isn’t and vice versa
  2. change a hidden input via JavaScript when the checkbox is clicked

What’s the best way to approach this? I would prefer a “pure” general solution, but since I need it for a project with , and , I tagged the question accordingly and if there is an easy way using these frameworks, that’s great too.

This works as intended:

<form id="the_form" method="post" action="">
    <input type="checkbox" id="the_checkbox" name="the_checkbox" value="foo" />
    document.forms.the_form.observe('submit', function() {
        document.getElementById('the_checkbox').checked = ! document.getElementById('the_checkbox').checked;

But you will see the checkbox status changing before the next page has loaded.



  1. You can use onsubmit event this way:

    $(".form-class").submit(function (e) {
      if (!$("#checkbox").is("checked"))
        return false;
    Login or Signup to reply.
  2. Ok so what i’ve understood is that you want to inverse the checkbox.

    If it’s checked dont send value with the form.

    If unchecked then send the value with the form.

    I only didn’t get if you want to submit the form on checkbox click.

    Make a hidden input with the same name that has the value.
    When the checkbox is checked then disable the hiddenbox.

    <input type='hidden' id='hiddenCheckboxValue' value='something' name='testbox'>
    <input type='checkbox' value='' name='testbox'>
            document.getElementById('hiddenCheckboxValue').disabled = true;
        } else {
           document.getElementById('hiddenCheckboxValue').disabled = false;
        //If you want to submit on checkbox click
        $( "#form" ).submit();

    //EDIT forgot that unchecked checkboxes dont get send. fixed i think

    Login or Signup to reply.
  3. you can dynamically add/remove elements to the form:

    $('the_form').observe('submit', function(event){
      $$('#the_form input[type=checkbox]').each(function(input){
        if (! input.checked) $('the_form').insert({top: new Element('input', {
             type: 'hidden'
           , class: 'dynamicInsert'
           , name:
           , value: 'off'
      $$('#the_form input.dynamicInsert').each(function(input){
      event.stop(); // don't know if .submit() accepts an event object as parameter
      return false;
    Login or Signup to reply.
Please signup or login to give your own answer.
Back To Top