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call function if attribute value has changed

This is not a duplicate, because the value of the input is changed by a function, not by user input.
Is it possible to call a function if the value of the attribute of an element has changed?
E.g. I use an input text with the id color and a button which opens a color picker. If I select a color then the color value is written into the input text with id color.
I try to detect if the value of the input text with id color has changed and call a function which sets the background-color of my input text to the selected color.
My attempt:
$("input#color").on
(
"change",
function()
{
console.log("SOMETHING HAS CHANGED");
var color = $("input#color").val();
$("input#color").css("background-color", color);
}
);
But SOMETHING HAS CHANGED is never shown.
I know I could solve this by using timers, but I think there must be a better solution.

Radio button REQUIRED if input field has content

I have a a reasonably quick problem to solve (I think). I have a form online and it validates the required content for the user's data, but has no validation on the first part of the form.
I've been asked however if I can make a radio button REQUIRED depending on whether an input field has been filled in.
The form can be found here:
http://www.elcorteingles.pt/reservas/livros_escolares/form.asp
So if the person start's filling in the input fields on the first line, that the radio buttons in the group become REQUIRED (for either the CDROM ou CADERNO but not both)

You can handle the focusout and blur events for the input:
$(function () {
// Handle every input type text.
// To select specific inputs, give them a common class and change the
// selector accordingly.
$("input[type=text]").on("focusout blur", function () {
// Check for inputs with class radio_btns which are in
// the parent element (li).
// Set their required property.
$(this).parent().find("input.radio_btns")
.prop("required", $(this).val().trim().length > 0);
});
});
Demo
jQuery reference (Tree Traversal)
jQuery reference (.prop())
jQuery reference (.focusout())
jQuery reference (.blur())

This will work. You can include the following JQuery code in the script tag, and also the JQuery cdn link in the head tag.
$(document).ready(function(){
$('#01titulo').focusout(function(){
if ($(this).val() !== "") {
$('[name="01caderno"]').prop('required', true);
} else {
$('[name="01caderno"]').prop('required', false);
}
alert($('[name="01caderno"]').attr('required'));
});
});

Try using the following js code its working:
$(document).ready(function(){
$(".titulo_books").each(function(){
$(this).focus(function(){
var radioChecked=0;
var currElemId = parseInt($(this).attr('id'));
var radioSelecterId = (currElemId>9) ? currElemId : "0"+currElemId;
$("input:radio[name="+radioSelecterId+"caderno]").each(function(){
if(radioChecked==0)
{
radioChecked==1;
$(this).attr("checked","checked");
}
});
});
});
});
I have checked it by executing this from console on your site and it seems to work fine. You can alter this in the way you want. I have checked one of the four available radio button. User can change the input value if required. Or you can also change the default radio button selected through my code.

Form validation causing wrong input in database from form field

I'm using a javascript that validates a form by radio buttons being checked, depending on which button is checked I want a value for that button submitted to MySQL but when I select a button it submits the button name to MySQL. changing the name of the button causes the script to stop working. How can I change the script so it allows the button value to post to MySQL instead of the button name?
jsFiddle
function ValidateForm(form) {
ErrorText = "";
if ((form.job_status[0].checked === false) && (form.job_status[1].checked === false)) {
alert("Before you can get a signature you must mark a selection.\n Is the work completed or do you need to return?");
return false;
}
if (ErrorText = "") {
form.submit();
}
}

job_status[0] ,job_status[1] means with name job_status two radio buttons exist.
If you change one of the radio buttons name either of job_status[0] job_status[1] one will exist.So you are getting exception
Instead of doing all that process by default select a radio button.That solves all your problems.I updated the link
see here

Binding Buttons to several text boxes actived based on size of values in text box

I am building a site where people can customize the shape of their product before they order it.
Ultimately there will be several buttons bound to four text boxes. As the user inputs higher values in the text box, the button that is activated changes so we know what size sheet of material will need to be ordered for this customer's design.
How can I create a button that is enabled/disabled based on the value placed in a text box?

You can use jQuery and try something like this:
First, give your buttons an attribute disabled="disabled", and then:
//Assuming they are typing, if it's a dropdown/select, see below
$('#input-id').on('keyup', function() {
if($(this).val() >= 10 && $(this).val() <= 20) { // If the value is between 10 and 20...
$('#button-id').removeAttr('disabled'); // Remove disabled attribute
} else { // If the value is not our keyword...
if(!$('#button-id').attr('disabled')) { // And the button is not disabled...
$('#button-id').attr('disabled', 'disabled'); // Readd disabled attribute
}
}
});
If you are using a dropdown or select box, use $("select option:selected").

How do I use jQuery to disable a form's submit button until every required field has been filled?

I have a form with multiple inputs, select boxes, and a textarea. I would like to have the submit button be disabled until all of the fields that I designate as required are filled with a value. And after they are all filled, should a field that WAS field get erased by the user, I would like the submit button to turn back to disabled again.
How can I accomplish this with jQuery?

Guess my first instinct would be to run a function whenever the user starts modifying any of the inputs. Something like this:
$('#submitBtn').prop('disabled', true);
$('.requiredInput').change(function() {
inspectAllInputFields();
});
We then would have a function that checks every input and if they're validated then enable the submit button...
function inspectAllInputFields(){
var count = 0;
$('.requiredInput').each(function(i){
if( $(this).val() === '') {
//show a warning?
count++;
}
if(count == 0){
$('#submitBtn').prop('disabled', false);
}else {
$('#submitBtn').prop('disabled', true);
}
});
}
You may also want to add a call to the inspect function on page-load that way if the input values are stored or your other code is populating the data it will still work correctly.
inspectAllInputFields();
Hope this helps,
~Matt

Here's something comprehensive, just because:
$(document).ready(function() {
$form = $('#formid'); // cache
$form.find(':input[type="submit"]').prop('disabled', true); // disable submit btn
$form.find(':input').change(function() { // monitor all inputs for changes
var disable = false;
$form.find(':input').not('[type="submit"]').each(function(i, el) { // test all inputs for values
if ($.trim(el.value) === '') {
disable = true; // disable submit if any of them are still blank
}
});
$form.find(':input[type="submit"]').prop('disabled', disable);
});
});
http://jsfiddle.net/mblase75/xtPhk/1/

Set the disabled attribute on the submit button. Like:
$('input:submit').attr('disabled', 'disabled');
And use the .change() event on your form fields.

Start with the button disabled (obviously). Bind an onkeyup event to each required text input, and an onchange or onclick to the select boxes (and any radio buttons/checkboxes), and when it fires, check whether all required inputs are filled. If so, enable the button. If not, disable it.
There is one loophole here, though. Users can delete the value of a text field without triggering the onkeyup event by using the mouse to "cut" the text out, or by holding down the delete/backspace key once they have deleted it all, and clicking the button before deleting it.
You can get around the second by either
disabling the button with onkeydown and checking if it is ok on onkeyup
checking for validity when the button is clicked

An idea from me:
Define a variable -with global scope- and add the value true- Write a submit function within your check the value above varibale. Evalue the the submit event only, if the value is true.
Write a function which ckecks all value from input fields and select fields. Checking the length of value to zero. if the value length of one field zero then change the value of the global variable to false.
After that, add to all input fields the event 'onKeydown' or 'onKeyUp' and to all select boxes the event 'onChange'.

I recommend taking a slightly different approach and using jquery's validation http://docs.jquery.com/Plugins/validation. The tactic you are suggesting is prone to security holes. The user could easily using firebug enable that button and then submit the form.
Using jquery validation is clean and it allows you to show error messages under the required fields if so desired on submit.