Develop Reference

How to preserve old input text value after the change in Javascript? [duplicate]

I have an input text in jQuery I want to know if it possible to get the value of that input text(type=number and type=text) before the onchange happens and also get the value of the same input input text after the onchange happens. This is using jQuery.
What I tried:
I tried saving the value on variable then call that value inside onchange but I am getting a blank value.

The simplest way is to save the original value using data() when the element gets focus. Here is a really basic example:
JSFiddle: http://jsfiddle.net/TrueBlueAussie/e4ovx435/
$('input').on('focusin', function(){
console.log("Saving value " + $(this).val());
$(this).data('val', $(this).val());
});
$('input').on('change', function(){
var prev = $(this).data('val');
var current = $(this).val();
console.log("Prev value " + prev);
console.log("New value " + current);
});
Better to use Delegated Event Handlers
Note: it is generally more efficient to use a delegated event handler when there can be multiple matching elements. This way only a single handler is added (smaller overhead and faster initialisation) and any speed difference at event time is negligible.
Here is the same example using delegated events connected to document:
$(document).on('focusin', 'input', function(){
console.log("Saving value " + $(this).val());
$(this).data('val', $(this).val());
}).on('change','input', function(){
var prev = $(this).data('val');
var current = $(this).val();
console.log("Prev value " + prev);
console.log("New value " + current);
});
JsFiddle: http://jsfiddle.net/TrueBlueAussie/e4ovx435/65/
Delegated events work by listening for an event (focusin, change etc) on an ancestor element (document* in this case), then applying the jQuery filter (input) to only the elements in the bubble chain then applying the function to only those matching elements that caused the event.
*Note: A a general rule, use document as the default for delegated events and not body. body has a bug, to do with styling, that can cause it to not get bubbled mouse events. Also document always exists so you can attach to it outside of a DOM ready handler :)

Definitely you will need to store old value manually, depending on what moment you are interested (before focusing, from last change).
Initial value can be taken from defaultValue property:
function onChange() {
var oldValue = this.defaultValue;
var newValue = this.value;
}
Value before focusing can be taken as shown in Gone Coding's answer. But you have to keep in mind that value can be changed without focusing.

Just put the initial value into a data attribute when you create the textbox, eg
HTML
<input id="my-textbox" type="text" data-initial-value="6" value="6" />
JQuery
$("#my-textbox").change(function () {
var oldValue = $(this).attr("data-initial-value");
var newValue = $(this).val();
});

I have found a solution that works even with "Select2" plugin:
function functionName() {
$('html').on('change', 'select.some-class', function() {
var newValue = $(this).val();
var oldValue = $(this).attr('data-val');
if ( $.isNumeric(oldValue) ) { // or another condition
// do something
}
$(this).attr('data-val', newValue);
});
$('select.some-class').trigger('change');
}

I found this question today, but I'm not sure why was this made so complicated rather than implementing it simply like:
var input = $('#target');
var inputVal = input.val();
input.on('change', function() {
console.log('Current Value: ', $(this).val());
console.log('Old Value: ', inputVal);
inputVal = $(this).val();
});
If you want to target multiple inputs then, use each function:
$('input').each(function() {
var inputVal = $(this).val();
$(this).on('change', function() {
console.log('Current Value: ',$(this).val());
console.log('Old Value: ', inputVal);
inputVal = $(this).val();
});

my solution is here
function getVal() {
var $numInput = $('input');
var $inputArr = [];
for(let i=0; i < $numInput.length ; i++ )
$inputArr[$numInput[i].name] = $numInput[i].value;
return $inputArr;
}
var $inNum = getVal();
$('input').on('change', function() {
// inNum is last Val
$inNum = getVal();
// in here we update value of input
let $val = this.value;
});

The upvoted solution works for some situations but is not the ideal solution. The solution Bhojendra Rauniyar provided will only work in certain scenarios. The var inputVal will always remain the same, so changing the input multiple times would break the function.
The function may also break when using focus, because of the ▲▼ (up/down) spinner on html number input. That is why J.T. Taylor has the best solution. By adding a data attribute you can avoid these problems:
<input id="my-textbox" type="text" data-initial-value="6" value="6" />

If you only need a current value and above options don't work, you can use it this way.
$('#input').on('change', () => {
const current = document.getElementById('input').value;
}

My business aim was removing classes form previous input and add it to a new one.
In this case there was simple solution: remove classes from all inputs before add
<div>
<input type="radio" checked><b class="darkred">Value1</b>
<input type="radio"><b>Value2</b>
<input type="radio"><b>Value3</b>
</div>
and
$('input[type="radio"]').on('change', function () {
var current = $(this);
current.closest('div').find('input').each(function () {
(this).next().removeClass('darkred')
});
current.next().addClass('darkred');
});
JsFiddle: http://jsfiddle.net/gkislin13/tybp8skL

if you are looking for select droplist, and jquery code would like this:
var preValue ="";
//get value when click select list
$("#selectList").click(
function(){
preValue =$("#selectList").val();
}
);
$("#selectList").change(
function(){
var curentValue = $("#selectList").val();
var preValue = preValue;
console.log("current:"+curentValue );
console.log("old:"+preValue );
}
);

How to listen to event from jQuery plugin which uses val()

I'm using cropin jQuery plugin in my project and going to pull updates for it in future so I don't want to change it's code.
Inside the plugin it changes the value of <input> element using val() function but doesn't instantly trigger the change event which means that I cannot listen to event using code like this:
on("change", function(){
//do something;
})
*details can be found here: .val() doesn't trigger .change() in jquery
Question: is there any workaround for this? How can I listen to change event without modifying the plugin code if plugin:
uses val() to modify the elements value
doesn't trigger change event following the val() call?

You could decorate the jquery val function.
edit: I couldn't resist making the suggested changes as it's such a good solution.
// jQuery plugin to decorate .val
(function( $ ){
var __val = $.fn.val,
// save the previous values to a hash table
values = {};
$.fn.val = function( newVal ){
// create a unique key based on tag offset id & class
var hashId = this.prop('nodeName').toLowerCase() + '[' + this.index() + ']' + '#' + this.attr('id') + '.' + this.attr('class').replace(' ', '.');
console.log('hashId', hashId);
if( newVal && ( !values[ hashId ] || ( values[ hashId ] !== newVal ) )) {
values[ hashId ] = newVal;
var ret = __val.apply(this, arguments);
this.trigger('change');
return ret;
}
console.log('no change');
return __val.apply(this, arguments);
}
})( jQuery );
var $input = $('#input'),
$changer = $('#changer');
$input.on('change', function(e){
console.log('changed: ' + this.value );
});
$changer.click(function(){
$input.val('something');
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="http://codepen.io/synthet1c/pen/WrQapG.js"></script>
<input id='input' class="some-input" type='text'>
<button id="changer">change</button>

I don't know if it works because I have never done it. However, according to: redefining-a-jquery-function
you could redefine jQuery's val function to trigger a change event.
In this way you won't have to touch the plugin and calling val() will fire an event every time it is called.
Sample code is included in the link provided.
EDIT: Answers to similar questions state that it is bad practice as sometimes doing so leads to an unpredictable behavior of jQuery.

See this http://jsfiddle.net/cqz2u8x8/1/ fiddle for different change events. You might want to try the on('input') event. This seems to trigger every time a real change in value has occured.
$("#testinput").on('input', function(e) {
$("#valuetyped-input").html(e.target.value)
});

How to bind a function to a select when is changed regardless how

I want to bind a function to a select with javascript. I can do it with onchange or .change(). However, it seems that my function is not being triggered if the change has done programmatically:
e.g.
<select id='selectId' onChange;"javascript:console.log('changed - onchange')">
jQuery( "#selectId" ).change(function() {
console.log( "changed - .change()" );
});
jQuery('#selectId').val("2").change() //(a)
jQuery('#selectId').val("1"); //(b)
If the user changes the select value, and in the case (a) the triggers will work. However, the second case will not be detected.
How can I make the binding, so it will detect the case (b) too.

Method $.fn.val doesn't trigger change event itself. The simplest thing you can do is to trigger it manually when you need it. If however you really want it to happen automatically you can extend valHook setter of the select element:
$.valHooks.select.set = function(orig) {
return function(el) {
var result = orig.apply(this, arguments);
$(el).trigger('change');
return result;
};
}($.valHooks.select.set);
This seems to work fine. You just take original hook and complement it with triggering code.
Demo: http://jsfiddle.net/cq07fL29/

Try using .trigger():
jQuery('#selectId').val("2").trigger("change");
EDIT:
Following the tip from #Rory McCrossan you can extend the val() function to trigger the event if it's a select element
// Save old val
var oldVal = $.fn.val;
$.fn.val = function(value) {
// Execute parent val()
obj = oldVal.apply(this, arguments);
// If it is a select
if(Object.prototype.toString.apply(this.get(0)) == '[object HTMLSelectElement]') {
// Trigger the event
this.trigger("change");
}
return obj;
};
$(document).ready(function() {
jQuery('#selectId').val("v3");
});
here is a working FIDDLE

Jquery creating checkboxs dynamically, and finding checked boxes

I have information that comes out of a database and gets put into a list with a checkbox by each element. This is how it is currently done:
function subjects(){
$.ajax({
url: "lib/search/search.subject.php",
async: "false",
success: function(response){
alert(response);
var responseArray = response.split(',');
for(var x=0;x<responseArray.length;x++){
$("#subjects").append("<br />");
$("#subjects").append(responseArray[x]);
$("#subjects").append("<input type='checkbox' />");
}
}
});
}
it works fine, but I need a way to pick up on if a checkbox is clicked, and if it is clicked then display which one was clicked, or if multiple ones are clicked.
I can't seem to find a way to pick up on the checkboxs at all.
the response variable is "math,science,technology,engineering"

Because you are populating the Checkboxes Dynamically you need to Delegate the event
$("#subjects").on("click", "input[type='checkbox']", function() {
if( $(this).is(":checked") ) {
alert('Checkbox checked')
}
});
To better capture the data it is better if you encase the corresponding data into a span , so that it can be easier to search..
$("#subjects").append('<span>'+responseArray[x] + '</span>');
$("#subjects").on("click", "input[type='checkbox']", function() {
var $this = $(this);
if( $this.is(":checked") ) {
var data = $this.prev('span').html();
alert('Current checkbox is : '+ data )
}
});

It would be best to give your dynamically injected checkboxes a class to target them better, but based on your code try:
$("#subjects").on("click", "input", function() {
if( $(this).is(":checked") ) {
// do something
}
});
Since your input elements are added dynamically, you need to use jQuery's .on() function to bind the click event to them. In your case you need to use .on() to bind to an element that exist in the DOM when the script is loaded. In your case, the element with the ID #subjects.
This note from the docs is mainly for machineghost who downvoted my answer for no apparent reason:
Event handlers are bound only to the currently selected elements; they
must exist on the page at the time your code makes the call to .on().
To ensure the elements are present and can be selected, perform event
binding inside a document ready handler for elements that are in the
HTML markup on the page. If new HTML is being injected into the page,
select the elements and attach event handlers after the new HTML is
placed into the page.

$('#subjects input[type=checkbox]').on('click',function(){
alert($(this).prop('checked'));
});
or the change event: in case someone uses a keyboard
$('#subjects input[type=checkbox]').on('change',function(){
alert($(this).prop('checked'));
});
simple fiddle example:http://jsfiddle.net/Dr8k8/
to get the array example use the index of the inputs
alert($(this).prop('checked') +'is'+ $(this).parent().find('input[type=checkbox]').index(this)+ responseArray[$(this).parent().find('input[type=checkbox]').index(this) ]);
simplified example: http://jsfiddle.net/Dr8k8/1/
EDIT: Just for an example, you could put the results in an array of all checked boxes and do somthing with that:
$('#subjects>input[type=checkbox]').on('change', function() {
var checklist = [];
$(this).parent().find('input[type=checkbox]').each(function() {
$(this).css('background-color', "lime");
var myindex = $(this).parent().find('input[type=checkbox]').index(this);
if ($(this).prop('checked') == true) {
checklist[myindex] = responseArray[myindex];
}
});
$('#currentlyChecked').text(checklist);
});
EDIT2:
I thought about this a bit and you can improve it by using .data() and query that or store it based on an event (my button called out by its id of "whatschecked")
var responseArray = ['math', 'science', 'technology', 'engineering'];// just for an example
var myList = '#subjects>input[type=checkbox]';//to reuse
for (var x = 0; x < responseArray.length; x++) {
// here we insert it all so we do not hit the DOM so many times
var iam = "<br />" + responseArray[x] + "<input type='checkbox' />";
$("#subjects").append(iam);
$(myList).last().data('subject', responseArray[x]);// add the data
}
var checklist = [];// holds most recent list set by change event
$(myList).on('change', function() {
checklist = [];
$(myList).each(function() {
var myindex = $(this).parent().find('input[type=checkbox]').index(this);
if ($(this).prop('checked') == true) {
checklist.push($(this).data('subject'));
alert('This one is checked:' + $(this).data('subject'));
}
});
});
// query the list we stored, but could query the checked list data() as well, see the .each() in the event handler for that example
$("#whatschecked").click(function() {
var numberChecked = checklist.length;
var x = 0;
for (x = 0; x < numberChecked; x++) {
alert("Number " + x + " is " + checklist[x] + " of " + numberChecked);
}
});
live example of last one: http://jsfiddle.net/Dr8k8/5/

The general pattern to do something when a checkbox input is clicked is:
$('input[type=checkbox]').click(function() {
// Do something
})
The general pattern to check whether a checkbox input is checked or not is:
var isItChecked = $('input[type=checkbox]').is(':checked');
In your particular case you'd probably want to do something like:
$('#subjects input[type=checkbox]').click(function() {
to limit the checkboxes involved to the ones inside your #subjects element.

How to know with jQuery that a "select" input value has been changed?

I know that there is the change event handling in jQuery associated with an input of type select. But I want to know if the user has selected another value in the select element ! So I don't want to run code when the user select a new element in the select but I want to know if the user has selected a different value !
In fact there are two select elements in my form and I want to launch an ajax only when the two select elements has been changed. So how to know that the two elements has been changed ?

You can specifically listen for a change event on your chosen element by setting up a binding in your Javascript file.
That only solves half your problem though. You want to know when a different element has been selected.
You could do this by creating a tracking variable that updates every time the event is fired.
To start with, give your tracking variable a value that'll never appear in the dropdown.
// Hugely contrived! Don't ship to production!
var trackSelect = "I am extremely unlikely to be present";
Then, you'll need to set up a function to handle the change event.
Something as simple as:-
var checkChange = function() {
// If current value different from last tracked value
if ( trackSelect != $('#yourDD').val() )
{
// Do work associated with an actual change!
}
// Record current value in tracking variable
trackSelect = $('#yourDD').val();
}
Finally, you'll need to wire the event up in document.ready.
$(document).ready(function () {
$('#yourDD').bind('change', function (e) { checkChange() });
});

First of all you may use select event handler (to set values for some flags). This is how it works:
$('#select').change(function () {
alert($(this).val());
});​
Demo: http://jsfiddle.net/dXmsD/
Or you may store the original value somewhere and then check it:
$(document).ready(function () {
var val = $('#select').val();
...
// in some event handler
if ($('#select').val() != val) ...
...
});

First you need to store previous value of the selected option, then you should check if new selected value is different than stored value.
Check out the sample!
$(document).ready(function() {
var lastValue, selectedValue;
$('#select').change(function() {
selectedValue = $(this).find(':selected').val();
if(selectedValue == lastValue) {
alert('the value is the same');
}
else {
alert('the value has changed');
lastValue = selectedValue;
}
});
});​

You can save the value on page load in some hidden field.
like
$(document).ready(function(){
$('hiddenFieldId').val($('selectBoxId').val());
then on change you can grab the value of select:
});
$('selectBoxId').change(function(){
var valChng = $(this).val();
// now match the value with hidden field
if(valChng == $('hiddenFieldId').val()){
}
});

$("select").change(function () {
var str = "";
$("select option:selected").each(function () {
str += $(this).text() + " ";
});
$("div").text(str);
})
.change();
http://docs.jquery.com/Events/change