Reactjs keypress regex?

Reactjs keypress regex? - javascript

Using ReactJS, I am trying to set a keypress regex listener. My code is below.
formation: function() {
var f1c = document.getElementsByClassName('f1t').value;
var validator = new RegExp('^[0-9.]*$');
var runner = validator.test(f1c);
var bling = document.getElementById('f1p2');
if (runner) {
alert("Vegetables");
} else {
alert("Fruits");
}
},
This is called from a separate function, like so.
something: function() {
return (
<input type="text" className="f1t" onKeyUp={this.formation}>something</p>
);
}
The problem is that the keyup event only runs as it should if I remove the if arguments, meaning that the keyup does work. However, there must be something off with my logic.
The code as shown above keeps showing Fruits when it is only supposed to show fruit if the value of f1c is not a number.

It's not good to directly access the DOM in React. Take a look at the following link to see best practices for handling form updates:
https://facebook.github.io/react/docs/forms.html
<input type="text" onKeyUp={this.formation}>something</p>
formation: function(event) {
var f1c = event.target.value;
...
}

When a user presses a key, and the event fires, the function will get a reference to the element and the key in the form of a React synthetic event.
formation: function(e) {
var theKeyPressed = e.charCode; // this is normalized for you by React
var theElementPressed = e.target;
var theValueOfTheElement = e.target.value;
// do your thing
},
something: function() {
return (
<input type="text" className="f1t" onKeyUp={this.formation}>something</p>
);
}
FYI, type="text" is redundant nowadays, it's the default.

Related

Why is the submit button value not included in the form data? [duplicate]

I'm trying to find the value of the submit button that triggered the form to submit
$("form").submit(function() {
});
I could possibly fire a $("input[type=submit]").click() event for each button and set some variable, but that seems less elegant than some how pulling the button off of the the form on submit.

I leveraged document.activeElement as sketched in this answer: How to get the focused element with jQuery?
$form.on('submit', function() {
var $btn = $(document.activeElement);
if (
/* there is an activeElement at all */
$btn.length &&
/* it's a child of the form */
$form.has($btn) &&
/* it's really a submit element */
$btn.is('button[type="submit"], input[type="submit"], input[type="image"]') &&
/* it has a "name" attribute */
$btn.is('[name]')
) {
console.log("Seems, that this element was clicked:", $btn);
/* access $btn.attr("name") and $btn.val() for data */
}
});
I take advantage of the fact, that the button is always the focused element after clicking it. This will not work, if you do a blur() right after the click.
#Doin has spotted another drawback. If a user submits the form via enter in a text field, the document.activeElement is not set. You'd need to watch out for this yourself, by handling keypress events in input[type="text"] and similar.
Update 2017-01: For my library Hyperform I chose not to use activeElement but to catch all events, that lead to form submission. The code for this is on Github.
If you happen to use Hyperform, this is how you would access the button that triggered the submit:
$(form).on('submit', function(event) {
var button = event.submittedVia;
});

I implemented this and I suppose it will do.
$(document).ready(function() {
$("form").submit(function() {
var val = $("input[type=submit][clicked=true]").val()
// DO WORK
});
and this is the submit button event that sets it up
$("form input[type=submit]").click(function() {
$("input[type=submit]", $(this).parents("form")).removeAttr("clicked");
$(this).attr("clicked", "true");
});
Thanks for the responses, but this isn't terribly inelegant...

There is now a standard submitter property in the submit event.
Already implemented in Firefox 75 and Chrome/Edge 81 !
document.addEventListener('submit',function(e){
console.log(e.submitter)
})
For browsers not supporting it, use this polyfill
Note: if you target older Browsers you need to polyfill other things like closest or matches. And ensure that the polyfill is loaded before adding your submit-events.
!function(){
var lastBtn = null
document.addEventListener('click',function(e){
if (!e.target.closest) return;
lastBtn = e.target.closest('button, input[type=submit]');
}, true);
document.addEventListener('submit',function(e){
if ('submitter' in e) return;
var canditates = [document.activeElement, lastBtn];
lastBtn = null;
for (var i=0; i < canditates.length; i++) {
var candidate = canditates[i];
if (!candidate) continue;
if (!candidate.form) continue;
if (!candidate.matches('button, input[type=button], input[type=image]')) continue;
e.submitter = candidate;
return;
}
e.submitter = e.target.querySelector('button, input[type=button], input[type=image]')
}, true);
}();

I created a test form and using Firebug found this way to get the value;
$('form').submit(function(event){
alert(event.originalEvent.explicitOriginalTarget.value);
});
Unfortunately, only Firefox supports this event.

Here's an approach that seems cleaner for my purposes.
First, for any and all forms:
$('form').click(function(event) {
$(this).data('clicked',$(event.target))
});
When this click event is fired for a form, it simply records the originating target (available in the event object) to be accessed later. This is a pretty broad stroke, as it will fire for any click anywhere on the form. Optimization comments are welcome, but I suspect it will never cause noticeable issues.
Then, in $('form').submit(), you can inquire what was last clicked, with something like
if ($(this).data('clicked').is('[name=no_ajax]')) xhr.abort();

According to this link, the Event object contains a field Event.target, which:
Returns a string representing the object that initiated the event.
I just created a page testing out what that value is, and it appears as though that representation is for the form itself, not for the button clicked. In other words, Javascript doesn't provide the facility to determine the clicked button.
As far as Dave Anderson's solution, it might be a good idea to test that in multiple browsers before using it. It's possible that it could work fine, but I can't say either way.

One clean approach is to use the click event on each form button.
Following is a html form with save,cancel and delete buttons:
<form name="formname" action="/location/form_action" method="POST">
<input name="note_id" value="some value"/>
<input class="savenote" type="submit" value="Save"/>
<input class="cancelnote" type="submit" value="Cancel"/>
<input class="deletenote" type="submit" value="Delete" />
</form>
Following is the jquery. I send the appropriate 'action' to the same server function depending on which button was clicked ('save' or 'delete'). If 'cancel', is clicked, I just reload the page.
$('.savenote').click(function(){
var options = {
data: {'action':'save'}
};
$(this).parent().ajaxSubmit(options);
});
$('.deletenote').click(function(){
var options = {
data: {'action':'delete'}
};
$(this).parent().ajaxSubmit(options);
});
$('.cancelnote').click(function(){
window.location.reload(true);
return false;
});

There's a submitter property for form's SubmitEvent. However, as of present time, this doesn't work on Safari.
<form id="form">
<button value="add" type="submit">Add</button>
<button value="remove" type="submit">Remove</button>
</form>
let form = document.getElementById('form');
form.onsubmit = (event) => {
e.preventDefault();
console.log(e.submitter.type);
}
A different approach that works across browsers. However, you have to rely on form element instead of the event object. This basically adds a 'submitter' property onto the form element object that can be referenced later on form submit.
<form id="form">
<button onclick="this.form.submitter = 'add'" type="submit">Add</button>
<button onclick="this.form.submitter = 'remove'" type="submit">Remove</button>
</form>
let form = document.getElementById('form');
form.onsubmit = (event) => {
e.preventDefault();
console.log(form.submitter);
}

I searched and found several ways to get the submit button name + value sent to the server using jQuery + AJAX. I didn't like them very much...
One of the bests was hunter's solution presented here!
But I wrote another one myself.
I want to share, because it is good, and, as I needed, it works also with forms loaded via ajax (after document.ready):
$(document).on('click', 'form input[type=submit]', function(){
$('<input type="hidden" />').appendTo($(this).parents('form').first()).attr('name', $(this).attr('name')).attr('value', $(this).attr('value'));
});
Simple! When the submit button is clicked, a hidden field is added to the form, using same name and value of the submit button.
EDIT: The version below is easier to read. Also, it takes care of removing previously appended hidden fields (in the case of submitting the same form twice, which is perfectly possible when using AJAX).
Improved code:
$(document).on('click', 'form input[type=submit]', function(){
var name = $(this).attr('name');
if (typeof name == 'undefined') return;
var value = $(this).attr('value');
var $form = $(this).parents('form').first();
var $input = $('<input type="hidden" class="temp-hidden" />').attr('name', name).attr('value', value);
$form.find('input.temp-hidden').remove();
$form.append($input);
});

( event )
function submForm(form,event){
var submitButton;
if(typeof event.explicitOriginalTarget != 'undefined'){ //
submitButton = event.explicitOriginalTarget;
}else if(typeof document.activeElement.value != 'undefined'){ // IE
submitButton = document.activeElement;
};
alert(submitButton.name+' = '+submitButton.value)
}
<form action="" method="post" onSubmit="submForm(this, event); return false;">

I did try some of the examples provided, but they didn't work for our purposes.
Here's a fiddle to show: http://jsfiddle.net/7a8qhofo/1/
I was faced with a similar issue, and this is how we solved the issue in our forms.
$(document).ready(function(){
// Set a variable, we will fill later.
var value = null;
// On submit click, set the value
$('input[type="submit"]').click(function(){
value = $(this).val();
});
// On data-type submit click, set the value
$('input[type="submit"][data-type]').click(function(){
value = $(this).data('type');
});
// Use the set value in the submit function
$('form').submit(function (event){
event.preventDefault();
alert(value);
// do whatever you need to with the content
});
});

Get the submitter object from the event object
You can simply get the event object when you submit the form. From that, get the submitter object. As below:
$(".review-form").submit(function (e) {
e.preventDefault(); // avoid to execute the actual submit of the form.
let submitter_btn = $(e.originalEvent.submitter);
console.log(submitter_btn.attr("name"));
}
I have explained in detail in this answer here: (https://stackoverflow.com/a/66334184/11320178)
Let me know if you have any doubts.

you can try this way with "event.originalEvent.x" and "event.originalEvent.y":
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></script>
<title>test</title>
</head>
<body>
<form id="is_a_form">
<input id="is_a_input_1" type="submit"><br />
<input id="is_a_input_2" type="submit"><br />
<input id="is_a_input_3" type="submit"><br />
<input id="is_a_input_4" type="submit"><br />
<input id="is_a_input_5" type="submit"><br />
</form>
</body>
</html>
<script>
$(function(){
$.fn.extend({
inPosition: function(x, y) {
return this.each(function() {
try{
var offset = $(this).offset();
if ( (x >= offset.left) &&
(x <= (offset.left+$(this).width())) &&
(y >= offset.top) &&
(y <= (offset.top+$(this).height())) )
{
$(this).css("background-color", "red");
}
else
{
$(this).css("background-color", "#d4d0c8");
}
}
catch(ex)
{
}
});
}
});
$("form").submit(function(ev) {
$("input[type='submit']").inPosition(ev.originalEvent.x ,ev.originalEvent.y);
return false;
});
});
</script>

jQuery doesn't seem to provide that data on the submit event. Looks like the method you proposed is your best bet.

Just another solution since no other met my requirements. The advantage is, that click and keypress (enter and space) are detected.
// Detects the Events
var $form = $('form');
$form.on('click keypress', 'button[type="submit"]', function (ev) {
// Get the key (enter, space or mouse) which was pressed.
if (ev.which === 13 || ev.which === 32 || ev.type === 'click') {
// Get the clicked button
var caller = ev.currentTarget;
// Input Validation
if (!($form.valid())) {
return;
}
// Do whatever you want, e.g. ajax...
ev.preventDefault();
$.ajax({
// ...
})
}
}
This worked best for me.

With a more specific event handler and JQuery, your event object is the button clicked. You can also get the delegating form from this event if needed.
$('form').on('click', 'button', function (e) {
e.preventDefault();
var
$button = $(e.target),
$form = $(e.delegateTarget);
var buttonValue = $button.val();
});
This Doc has everything you need to get started.
JQuery Doc.

I write this function that helps me
var PupulateFormData= function (elem) {
var arr = {};
$(elem).find("input[name],select[name],button[name]:focus,input[type='submit']:focus").each(function () {
arr[$(this).attr("name")] = $(this).val();
});
return arr;
};
and then Use
var data= PupulateFormData($("form"));

In working with web components where form elements are in the shadowRoot I adapted Tobias Buschor's excellent polyfill as follows to work in the following way via an imported module. Note this only provides compatibility in evergreen clients--edge, safari, chrome, firefox. Also, as noted by Mikko Rantalainen, this doesn't follow (and I/we can update at some point to follow) https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#concept-form-submit
if( !('SubmitEvent' in self && 'submitter' in SubmitEvent.prototype) ){
// polyfill SubmitEvent.submitter (a Safari issue as-of 2021)
// https://developer.mozilla.org/docs/Web/API/SubmitEvent
const submitter = Symbol.for('submitter');
Event[ submitter ] = null;
const submitterSelector = 'input[type=submit], input[type=image], input[type=button], button';
Object.defineProperty(Event.prototype, 'submitter', {
get: function(){
if('submit' === this.type){
let node = Event[ submitter ];
const form = this.target;
if(!node || !form.contains(node)){
node = form.querySelector(submitterSelector);
}
// always return a node, default as though form.submit called
return node || form;
}
return undefined;
},
set: function(value){
if('submit' === this.type){
this.submitter = value;
}
}
});
self.addEventListener('click', function polyfill_SubmitEvent_submitter_click(event){
const node = event.composedPath()[0];
const closest = node.closest?.(submitterSelector) ?? null;
Event[ submitter ] = closest;
}, true);
}

$(document).ready(function() {
$( "form" ).submit(function (event) {
// Get the submit button element
let submit_button = event.handleObj;
//submit button has the object of the use clicked button
});
}

You can obtain the button id of the following HTML code:
<form id="theForm" action="" method="POST">
<button name="sbtn" id="sbtn" value="Hey button" type="submit">Submit</button>
</form>
using the following JavaScript (leveraging on the .val() attribute):
$('#theForm').on('click', 'button', function (e) {
e.preventDefault();
var
$button = $(e.target),
$form = $(e.delegateTarget);
var buttonValue = $button.val();
});

Without jquery
submit(e){
console.log(e.nativeEvent.submitter)
}

I was finally able to find a complete and easy answer to the question : How can I get the button that caused the submit from the form submit event ?
I'll give you a simple example :
CODE HTML : The form
<form id="myForm" enctype="multipart/form-data" method="post">
...
all input, select, textarea ...
....
<button id="bt1" value="add" type="submit">Add</button>
<button id="bt2" value="back" type="submit">Back</button>
<button id="bt3" value="remove" type="submit">Remove</button>
<button id="bt4" value="register" type="submit">Register</button>
</form>
CODE JAVASCRIPT : event listener and actions
var myFctSubmit = function(event){
var myTarget = event.target || event.srcElement;
var myButton = event.originalEvent.submitter;
var balise_form = $(myTarget).attr('id');
var balise_button = $(myButton).attr('id');
//Now you know the button and
//you can apply the script you want...
//here in this exemple :
//balise_form = myForm
//balise_button = {button that you click}
}
$('#myForm').bind('submit',myFctSubmit);
Therefore, the solution to this problem is to fetch the following element :
event.originalEvent.submitter
Good luck everyone

Javascript get event from this

I am trying to move from inline onkeyup event and changed my input from
<input name="some1" id="some1" onkeyup="ajax_autocomplete('some1',this.value,event);">
to
<input name="some1" id="some1" class="autoc">
and after page load
var acinputs = document.querySelectorAll('.autoc');
for(var i=0; field=acinputs[i]; i++)
{
field.onkeyup = function() {update.call(this);}
function update()
{
var text = this.value;
// How to get keycode now from event?
// Before: var kc=event.which;if(kc==undefined){kc=event.keyCode}
}
}
My problem is that while I was getting event data inline like keycode from the event before but I do not know how to get it from event now? this.value gives me the text entered in the input however this.event does not work! I know this.event is not the proper way of getting event from this !
I am not using jQuery.

Add event as parameter
In my example event is referred to ev.
field.onkeyup = function(ev) {update.call(this, ev);}
function update(th, ev)
{
var text = th.value;
var kc=ev.which;
if(kc==undefined) {
kc=ev.keyCode
}
}

Using substring within input field

I'm using an ID scanner that acts as a keyboard input and I want an input field to listen for the value and substring (or slice) out unnecessary, extra values.
Currently, the ID scanner formats numbers like this: ;708089113=0184?
I want to grab only the 708089113. I want to remove the semi-colon and everything after the 3.
I'm just not sure how to do this automatically. The stripped value should appear in the field before submitting.
Javascript:
var suid = document.getElementById("SUID").value;
var stripSUID = suid.substring(1,10);
document.getElementById("SUID").value = stripSUID;
HTML:
<input name="SUID" id="SUID" type="text" value="">
JSFiddle Link

You can use jQuery for this.
HTML:
<input name="suid" id="suid" type="text" value="">
JavaScript:
$(function() {
$('#suid').change(function() {
var suid = $(this).val();
var stripSUID = suid.split('=');
var stringLength = stripSUID[0].length;
var returnValue = stripSUID[0].substr(1, stringLength);
$(this).val(returnValue);
});
});
jsFiddle update: http://jsfiddle.net/jhjr288o/4/

So you're asking how to listen for a change to the <input>?
var elm = document.getElementById('SUID');
elm.addEventListener('change', function (e) {
var s = this.value, i = s.indexOf('=');
if (i !== -1) {
s = s.slice(1, i);
this.value = s;
}
});
DEMO
The change event fires when the element loses focus
The input event fires every time oldvalue !== newvalue (i.e. for every char typed)
Also note, this code must be run after the Element exists, i.e. wait for the Window's load event

What is the best way to prevent the same trigger function from executing twice?

A trigger can be applied at the form level and/or at the item level. What is the best way for it not to be executed the second time?
<form id='f'>
<input id='i' type='text' />
</form>
<script>
validate = function(e) { ... }
reformat = function(e) { ... }
document.getElementById('f').addListener('change',validate,true);
document.getElementById('i').addListener('change',validate,true);
document.getElementById('i').addListener('change',reformat,true);
</script>
Context: a data dictionary says item i needs to be validated immediately, and the app writer says all items in the form should be validated immediately.
It's the same function, usually called once, but sometimes twice.
What's the best way to keep the validate function from being executing twice?
Note: e.stopPropagation() stops all further calls on the click event, so that the reformat trigger is no longer called.

You can add a prop in the event param to make sure it runs once:
validate = function(e) { if (e.done) return; /* code */ e.done = true; }
document.getElementById('f').addListener('change',validate,true);
document.getElementById('i').addListener('change',validate,true);
DEMO
Although I don't see why you're binding the event twice
EDIT: For cross browserness (read: IE) change it to this:
validate = function(e) {
if ((e = e || window.event).done) return;
/* code */
e.done = true;
}
document.getElementById('f').addListener('change',validate,true);
document.getElementById('i').addListener('change',validate,true);
Edited DEMO

Basic idea (based on http://www.quirksmode.org/js/events_order.html):
function cancelBubbling(e) {
if (!e) var e = window.event;
e.cancelBubble = true;
if (e.stopPropagation) e.stopPropagation();
}
var validate = function(e) {
cancelBubbling(e); // important!
...
};

What is the best way to track changes in a form via javascript?

I'd like to track changes in inputs in a form via javascript. My intent is (but not limited) to
enable "save" button only when something has changed
alert if the user wants to close the page and something is not saved
Ideas?

Loop through all the input elements, and put an onchange handler on each. When that fires, set a flag which lets you know the form has changed. A basic version of that would be very easy to set up, but wouldn't be smart enough to recognize if someone changed an input from "a" to "b" and then back to "a". If it were important to catch that case, then it'd still be possible, but would take a bit more work.
Here's a basic example in jQuery:
$("#myForm")
.on("input", function() {
// do whatever you need to do when something's changed.
// perhaps set up an onExit function on the window
$('#saveButton').show();
})
;

Text form elements in JS expose a .value property and a .defaultValue property, so you can easily implement something like:
function formChanged(form) {
for (var i = 0; i < form.elements.length; i++) {
if(form.elements[i].value != form.elements[i].defaultValue) return(true);
}
return(false);
}
For checkboxes and radio buttons see whether element.checked != element.defaultChecked, and for HTML <select /> elements you'll need to loop over the select.options array and check for each option whether selected == defaultSelected.
You might want to look at using a framework like jQuery to attach handlers to the onchange event of each individual form element. These handlers can call your formChanged() code and modify the enabled property of your "save" button, and/or attach/detach an event handler for the document body's beforeunload event.

Here's a javascript & jquery method for detecting form changes that is simple. It disables the submit button until changes are made. It detects attempts to leave the page by means other than submitting the form. It accounts for "undos" by the user, it is encapsulated within a function for ease of application, and it doesn't misfire on submit. Just call the function and pass the ID of your form.
This function serializes the form once when the page is loaded, and again before the user leaves the page. If the two form states are different, the prompt is shown.
Try it out: http://jsfiddle.net/skibulk/ev5rE/
function formUnloadPrompt(formSelector) {
var formA = $(formSelector).serialize(), formB, formSubmit = false;
// Detect Form Submit
$(formSelector).submit( function(){
formSubmit = true;
});
// Handle Form Unload
window.onbeforeunload = function(){
if (formSubmit) return;
formB = $(formSelector).serialize();
if (formA != formB) return "Your changes have not been saved.";
};
// Enable & Disable Submit Button
var formToggleSubmit = function(){
formB = $(formSelector).serialize();
$(formSelector+' [type="submit"]').attr( "disabled", formA == formB);
};
formToggleSubmit();
$(formSelector).change(formToggleSubmit);
$(formSelector).keyup(formToggleSubmit);
}
// Call function on DOM Ready:
$(function(){
formUnloadPrompt('form');
});

Try
function isModifiedForm(form){
var __clone = $(form).clone();
__clone[0].reset();
return $(form).serialize() == $(__clone).serialize();
}
Hope its helps ))

If your using a web app framework (rails, ASP.NET, Cake, symfony), there should be packages for ajax validation,
http://webtecker.com/2008/03/17/list-of-ajax-form-validators/
and some wrapper on onbeforeunload() to warn users taht are about to close the form:
http://pragmatig.wordpress.com/2008/03/03/protecting-userdata-from-beeing-lost-with-jquery/
Detecting Unsaved Changes

I answered a question like this on Ars Technica, but the question was framed such that the changes needed to be detected even if the user does not blur a text field (in which case the change event never fires). I came up with a comprehensive script which:
enables submit and reset buttons if field values change
disables submit and reset buttons if the form is reset
interrupts leaving the page if form data has changed and not been submitted
supports IE 6+, Firefox 2+, Safari 3+ (and presumably Opera but I did not test)
This script depends on Prototype but could be easily adapted to another library or to stand alone.
$(document).observe('dom:loaded', function(e) {
var browser = {
trident: !!document.all && !window.opera,
webkit: (!(!!document.all && !window.opera) && !document.doctype) ||
(!!window.devicePixelRatio && !!window.getMatchedCSSRules)
};
// Select form elements that won't bubble up delegated events (eg. onchange)
var inputs = $('form_id').select('select, input[type="radio"], input[type="checkbox"]');
$('form_id').observe('submit', function(e) {
// Don't bother submitting if form not modified
if(!$('form_id').hasClassName('modified')) {
e.stop();
return false;
}
$('form_id').addClassName('saving');
});
var change = function(e) {
// Paste event fires before content has been pasted
if(e && e.type && e.type == 'paste') {
arguments.callee.defer();
return false;
}
// Check if event actually results in changed data
if(!e || e.type != 'change') {
var modified = false;
$('form_id').getElements().each(function(element) {
if(element.tagName.match(/^textarea$/i)) {
if($F(element) != element.defaultValue) {
modified = true;
}
return;
} else if(element.tagName.match(/^input$/i)) {
if(element.type.match(/^(text|hidden)$/i) && $F(element) != element.defaultValue) {
modified = true;
} else if(element.type.match(/^(checkbox|radio)$/i) && element.checked != element.defaultChecked) {
modified = true;
}
}
});
if(!modified) {
return false;
}
}
// Mark form as modified
$('form_id').addClassName('modified');
// Enable submit/reset buttons
$('reset_button_id').removeAttribute('disabled');
$('submit_button_id').removeAttribute('disabled');
// Remove event handlers as they're no longer needed
if(browser.trident) {
$('form_id').stopObserving('keyup', change);
$('form_id').stopObserving('paste', change);
} else {
$('form_id').stopObserving('input', change);
}
if(browser.webkit) {
$$('#form_id textarea').invoke('stopObserving', 'keyup', change);
$$('#form_id textarea').invoke('stopObserving', 'paste', change);
}
inputs.invoke('stopObserving', 'change', arguments.callee);
};
$('form_id').observe('reset', function(e) {
// Unset form modified, restart modified check...
$('reset_button_id').writeAttribute('disabled', true);
$('submit_button_id').writeAttribute('disabled', true);
$('form_id').removeClassName('modified');
startObservers();
});
var startObservers = (function(e) {
if(browser.trident) {
$('form_id').observe('keyup', change);
$('form_id').observe('paste', change);
} else {
$('form_id').observe('input', change);
}
// Webkit apparently doesn't fire oninput in textareas
if(browser.webkit) {
$$('#form_id textarea').invoke('observe', 'keyup', change);
$$('#form_id textarea').invoke('observe', 'paste', change);
}
inputs.invoke('observe', 'change', change);
return arguments.callee;
})();
window.onbeforeunload = function(e) {
if($('form_id').hasClassName('modified') && !$('form_id').hasClassName('saving')) {
return 'You have unsaved content, would you really like to leave the page? All your changes will be lost.';
}
};
});

I would store each fields value in a variable when the page loads, then compare those values when the user unloads the page. If any differences are detected you will know what to save and better yet, be able to specifically tell the user what data will not be saved if they exit.
// this example uses the prototype library
// also, it's not very efficient, I just threw it together
var valuesAtLoad = [];
var valuesOnCheck = [];
var isDirty = false;
var names = [];
Event.observe(window, 'load', function() {
$$('.field').each(function(i) {
valuesAtLoad.push($F(i));
});
});
var checkValues = function() {
var changes = [];
valuesOnCheck = [];
$$('.field').each(function(i) {
valuesOnCheck.push($F(i));
});
for(var i = 0; i <= valuesOnCheck.length - 1; i++ ) {
var source = valuesOnCheck[i];
var compare = valuesAtLoad[i];
if( source !== compare ) {
changes.push($$('.field')[i]);
}
}
return changes.length > 0 ? changes : [];
};
setInterval(function() { names = checkValues().pluck('id'); isDirty = names.length > 0; }, 100);
// notify the user when they exit
Event.observe(window, 'beforeunload', function(e) {
e.returnValue = isDirty ? "you have changed the following fields: \r\n" + names + "\r\n these changes will be lost if you exit. Are you sure you want to continue?" : true;
});

I've used dirtyforms.js. Works well for me.
http://mal.co.nz/code/jquery-dirty-forms/

To alert the user before closing, use unbeforeunload:
window.onbeforeunload = function() {
return "You are about to lose your form data.";
};

I did some Cross Browser Testing.
On Chrome and Safari this is nice:
<form onchange="validate()">
...
</form>
For Firefox + Chrome/Safari I go with this:
<form onkeydown="validate()">
...
<input type="checkbox" onchange="validate()">
</form>
Items like checkboxes or radiobuttons need an own onchange event listener.

Attach an event handler to each form input/select/textarea's onchange event. Setting a variable to tell you if you should enable the "save" button. Create an onunload hander that checks for a dirty form too, and when the form is submitted reset the variable:
window.onunload = checkUnsavedPage;
var isDirty = false;
var formElements = //Get a reference to all form elements
for(var i = 0; len = formElements.length; i++) {
//Add onchange event to each element to call formChanged()
}
function formChanged(event) {
isDirty = false;
document.getElementById("savebtn").disabled = "";
}
function checkUnsavedPage() {
if (isDirty) {
var isSure = confirm("you sure?");
if (!isSure) {
event.preventDefault();
}
}
}

Here's a full implementation of Dylan Beattie's suggestion:
Client/JS Framework for "Unsaved Data" Protection?
You shouldn't need to store initial values to determine if the form has changed, unless you're populating it dynamically on the client side (although, even then, you could still set up the default properties on the form elements).

You can also check out this jQuery plugin I built at jQuery track changes in forms plugin
See the demo here and download the JS here

If you are open to using jQuery, see my answer a similar question:
Disable submit button unless original form data has changed.

I had the same challenge and i was thinking of a common solution. The code below is not perfect, its from initial r&d. Following are the steps I used:
1) Move the following JS to a another file (say changeFramework.js)
2) Include it in your project by importing it
3) In your html page, whichever control needs monitoring, add the class "monitorChange"
4) The global variable 'hasChanged' will tell, if there is any change in the page you working on.
<script type="text/javascript" id="MonitorChangeFramework">
// MONITOR CHANGE FRAMEWORK
// ALL ELEMENTS WITH CLASS ".monitorChange" WILL BE REGISTERED FOR CHANGE
// ON CHANGE IT WILL RAISE A FLAG
var hasChanged;
function MonitorChange() {
hasChanged = false;
$(".monitorChange").change(function () {
hasChanged = true;
});
}
Following are the controls where I used this framework:
<textarea class="monitorChange" rows="5" cols="10" id="testArea"></textarea></br>
<div id="divDrinks">
<input type="checkbox" class="chb monitorChange" value="Tea" />Tea </br>
<input type="checkbox" class="chb monitorChange" value="Milk" checked='checked' />Milk</br>
<input type="checkbox" class="chb monitorChange" value="Coffee" />Coffee </br>
</div>
<select id="comboCar" class="monitorChange">
<option value="volvo">Volvo</option>
<option value="saab">Saab</option>
<option value="mercedes">Mercedes</option>
<option value="audi">Audi</option>
</select>
<button id="testButton">
test</button><a onclick="NavigateTo()">next >>> </a>
I believe there can be huge improvement in this framework. Comment/Changes/feedbacks are welcome. :)

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