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Dropdown option "change" not working if change event is unbound and then rebound

I'm facing this weird issue with off() and on() event binding to a select dropdown:
If I unbind and then rebind the change event to the select dropdown I won't be able to change the dropdown shown value. In other words, the selected value is not updated properly in the dropdown, even if the change event is triggered.
If I remove the off() part, leaving only the event bounding with on(), everything works fine but obviously I'm not able to prevent the binding of the same event more than once.
See a live example here http://jsfiddle.net/z7o11exs/
Test case:
use the dropdown (it works! the selected value is correctly show in the dropdown)
refresh page. click on the first button (off/on) and then use the dropdown. It does not work properly as the selected value does not change
refresh page. click on the second button (only on) and then use the dropdown. It does work as expected. side effect: clicking n times on the 2nd button bounds n times the change event to the dropdown element
Here's the code:
//--- This binds the event to the element
function bindEvent(){
$("#myselect").on("change", function(){
console.log("change");
});
}
//--- remove any change event previously added, then rebind it
function rebindEvent(){
$("#myselect").off("change").on("change", function(){
console.log("change");
});
}
Thanks in advance

Try to use namespacing:
//--- This binds the event to the element
function bindEvent(){
$("#myselect").on("change.something", function(){
console.log("change");
});
}
//--- remove any change event previously added, then rebind it
function rebindEvent(){
$("#myselect").off("change.something").on("change", function(){
console.log("change");
});
}
As #Karl said, using namespace is to:
Giving a name to your event allow you to identify that event. So when using .off, you can target a specific event to turn off.

You have to call .selectmenu("refresh") when you remove change binding. Because by default, change is attached to selectmenu as mentioned here. So if you remove it, you interrupt jQuery Mobile widget from "refreshing" to visually display the value.
See it working here.
function rebindEvent(){
$("#myselect").off("change").on("change", function(){
$(this).selectmenu("refresh");
});
}

jQuery change event is not working as expected

I have added change event on the input field so that whenever user enters the text into it, so other task should happen, it works but when i click outside the input field.I don't know whether it is default behavior or i am doing some thing wrong. I tried using keyup and keydown events and it works as expect.
Please suggest.
Here is my code:
$("#mobile-number").on('change',function(){
// some other code
});

The change event fires when an elements value changes.
For select boxes, checkboxes, and radio buttons, the event is fired immediately when the user makes a selection with the mouse, but for the other element types the event is deferred until the element loses focus.
In other words, on an input, the change event fires when the element loses focus, not when you type, and that is the default behaviour.
That's why there are key events as well, and on modern browsers you can catch most changes to an input with the input event
$("#mobile-number").on('input',function(){ ...

Yes, it is the desired behavior.
Change Event
The change event is fired for , , and
elements when a change to the element's value is committed by the
user. Unlike the input event, the change event is not necessarily
fired for each change to an element's value.
Depending on the kind of form element being changed and the way the
user interacts with the element, the change event fires at a different
moment:
When the element is activated (by clicking or using the keyboard) for and ;
When the user commits the change explicitly (e.g. by selecting a value from a 's dropdown with a mouse click, by selecting a
date from a date picker for , by selecting a file
in the file picker for , etc.);
When the element loses focus after its value was changed, but not commited (e.g. after editing the value of or ).

Try using input event:
$(function() {
$("#mobile-number").on('input', function() {
$("#copy").val(this.value);
});
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<input type='text' id='mobile-number' />
<input type='text' id='copy' readonly/>

Try this:( If i really understand your problem )
jQuery(document).on('change', '#mobile-number', function() {
// some other code
});
for type event:
jQuery(document).on('keyup', '#mobile-number', function() {
// some other code
});

You should provide your selector to the .on function:
$(document).on('change', '#mobile-number', function() {
// some other code
});

While setting value for dropdown in jQuery, will .change function get invoked?

Whenever we are setting values for a dropdown element, using either
$("#dropDownId").val(giveAValueHere);
or
$('#dropDownId option:contains("' + giveTheTextHere + '")').prop('selected', true);
will the .change() function for that element get invoked?
Assume that the ,change() function for the dropdown is defined and the
giveTheTextHere element is always present in the dropdown menu.

Changing an element from javascript does not fire the change event. You need to trigger it:
$("body").on("change", "#dropDownId", function () {
alert("Changed");
});
or:
$("#dropDownId").val(giveAValueHere).change();

The change event handler wont invoke if you change value through code, although you can trigger change event after changing the value.
$("#dropDownId").val(giveAValueHere).trigger("change");
or
$("#dropDownId").val(giveAValueHere).change();

jquery `on change` doesn't recognize when you set textbox value programmatically

I want to clear out a textbox when I call:
$('#textBox').val(''); or $('#textBox').empty();
Originally, when I would manually backspace and delete the text out of the text box, the on change function would fire. If I run $('#textBox').val('') above, on change does not fire:
$(document).ready(function() {
$('#textBox').on('change', function(){
Why is this?

Use trigger, like this:
$("#testBox").val("").trigger("change");

When you change the value programmatically, just trigger the change event using trigger.
$("#myid").trigger("change");

It's not jQuery that doesn't fire the event, it's the browser. If you look it up in the specs you'll see the definition of the change event:
change
The change event occurs when a control loses the input focus and its value has been
modified since gaining focus. This event is valid for INPUT, SELECT, and
TEXTAREA. element.
Bubbles: Yes
Cancelable: No
Context Info: None
As already posted, your problem can be mitigated by triggering the event manually via trigger().

Detecting input change in jQuery?

When using jquery .change on an input the event will only be fired when the input loses focus
In my case, I need to make a call to the service (check if value is valid) as soon as the input value is changed. How could I accomplish this?

UPDATED for clarification and example
examples: http://jsfiddle.net/pxfunc/5kpeJ/
Method 1. input event
In modern browsers use the input event. This event will fire when the user is typing into a text field, pasting, undoing, basically anytime the value changed from one value to another.
In jQuery do that like this
$('#someInput').bind('input', function() {
$(this).val() // get the current value of the input field.
});
starting with jQuery 1.7, replace bind with on:
$('#someInput').on('input', function() {
$(this).val() // get the current value of the input field.
});
Method 2. keyup event
For older browsers use the keyup event (this will fire once a key on the keyboard has been released, this event can give a sort of false positive because when "w" is released the input value is changed and the keyup event fires, but also when the "shift" key is released the keyup event fires but no change has been made to the input.). Also this method doesn't fire if the user right-clicks and pastes from the context menu:
$('#someInput').keyup(function() {
$(this).val() // get the current value of the input field.
});
Method 3. Timer (setInterval or setTimeout)
To get around the limitations of keyup you can set a timer to periodically check the value of the input to determine a change in value. You can use setInterval or setTimeout to do this timer check. See the marked answer on this SO question: jQuery textbox change event or see the fiddle for a working example using focus and blur events to start and stop the timer for a specific input field

If you've got HTML5:
oninput (fires only when a change actually happens, but does so immediately)
Otherwise you need to check for all these events which might indicate a change to the input element's value:
onchange
onkeyup (not keydown or keypress as the input's value won't have the new keystroke in it yet)
onpaste (when supported)
and maybe:
onmouseup (I'm not sure about this one)

With HTML5 and without using jQuery, you can using the input event:
var input = document.querySelector('input');
input.addEventListener('input', function()
{
console.log('input changed to: ', input.value);
});
This will fire each time the input's text changes.
Supported in IE9+ and other browsers.
Try it live in a jsFiddle here.

As others already suggested, the solution in your case is to sniff multiple events.
Plugins doing this job often listen for the following events:
$input.on('change keydown keypress keyup mousedown click mouseup', handler);
If you think it may fit, you can add focus, blur and other events too.
I suggest not to exceed in the events to listen, as it loads in the browser memory further procedures to execute according to the user's behaviour.
Attention: note that changing the value of an input element with JavaScript (e.g. through the jQuery .val() method) won't fire any of the events above.
(Reference: https://api.jquery.com/change/).

// .blur is triggered when element loses focus
$('#target').blur(function() {
alert($(this).val());
});
// To trigger manually use:
$('#target').blur();

If you want the event to be fired whenever something is changed within the element then you could use the keyup event.

There are jQuery events like keyup and keypress which you can use with input HTML Elements.
You could additionally use the blur() event.

This covers every change to an input using jQuery 1.7 and above:
$(".inputElement").on("input", null, null, callbackFunction);