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on change event fires only once

i'm trying to update cart whenever product quantity is changed. but jquery code is stop working after first time updating cart items.
here is jquery code
jQuery(document).ready(function($){
$("input.qty").on('keyup change click',function(){
$('input[name=update_cart]').trigger('click');
});
});

Please try following code.
jQuery(document).ready(function($){
$(document).on('keyup change click','input.qty', function() {
$('input[name=update_cart]').trigger('click');
});
});
let me know if you require further information.

Use the input event
jQuery(document).ready(function($){
$("input.qty").on('input',function(){
$(this).closest('form').submit();
});
});

Your code is working. See result of below code.
jQuery(document).ready(function($){
var count = 0;
$("input.qty").on('keyup change click',function(){
$('input[name=update_cart]').trigger('click');
count++;
});
$('input[name=update_cart]').click(function(e){
$(this).val('Click called '+count);
});
});
<script src="http://code.jquery.com/jquery-1.10.2.js"></script>
<input class="qty" name="test"/>
<input name="update_cart"/>

JS click in a Jquery function on load

I have a JS function that I want to automatic click in a jquery.click link when page loads.
How can I make it work?
Fiddle
When page loads I want to see the alert, no click in the link needed.
js:
window.onload = function(){
document.getElementsByClassName("c").click();
}
$(".c").click(function(){
alert("ok");
});
html:
test

you need to attach click event before trigger event.
DEMO
Change
document.getElementsByClassName("c")
to
document.getElementsByClassName("c")[0]
Use Below code
$(document).ready(function(){
$(".c").click(function(){
alert("ok");
});
});
window.onload = function(){
document.getElementsByClassName("c")[0].click();
// Or use jQuery trigger
// $(".c").trigger('click')
}

DEMO HERE
trigger click on document.ready
$('document').ready(function(){
$(".c").click(function(){
alert("ok");
});
$('.c').trigger('click');
});

Trigger event right after you create handler
$(function(){
$(".c").click(function(){
alert("ok");
}).click();
});
DEMO

Try this way
$(document).ready(function(){
$(".c").trigger('click');
});

getElementsByClassName Returns an array-like object of all child elements which have all of the given class names. When called on the document object, the complete document is searched, including the root node.
To assign a click handler, either you will have to iterate through nodelist or just assign event to first element
Try this:
window.onload = function () {
document.getElementsByClassName("c")[0].click();
};
$(".c").click(function () {
alert("ok");
});

So you can push your alert into a function :
function callAlert() {
alert('a');
}
And you can change the event click like this :
$(".c").click(callAlert);
Finally you can call the alert function when page loads like this :
$('document').ready(function(){
callAlert(); // call here
});
Code :
$('document').ready(function(){
callAlert();
$(".c").click(callAlert);
});
function callAlert() {
alert('a');
}

I need a button click instead of setInterval

I found this code but for my site I need a button instad of setInterval. I tried jquery("#btn").click(function(){}) but can't get it working.
<script>
jQuery().ready(function(){
setInterval("getResult()",1000); //set theinterval for the update
});
function getResult(){
jQuery.post("update.php", function(data) {
jQuery("#readings").html(data);
});
}
</script>
<div id="readings"></div>

You need to add a click event listener to a button. The jsfiddle below should help you. This can be done using pure JavaScript but as you suggested jQuery.
<button id="test">Test</button>
$("#test").click(function() {
alert("Click event!");
});
http://jsfiddle.net/89987ps1/

You can call your function like this:
<button onclick="getResult()" >Get result</button>

jQuery getting data attribute not working

I have a script that produces a number of buttons with a class and I want it to alert the data attribute on click but it's not working.
Here is the output of HTML
<button class="request box-button" data-value="18492500814">Request</button>
jQuery code
$(document).ready(function(){
$('.request').each(function () {
var photoID = $(this);
photoID.click(function () {
alert($(this).data('value'));
});
});
});

Since your elements don't exist when the page loads, the event won't be bound to them. Fix that by using event delegation:
$(document).ready(function(){
$(document).on('click','.request', function () {
alert($(this).data('value'));
});
});
JS Fiddle demo with dynamically generated elements
Note: Here, I used $(document).on() because I don't have your page's structure. But if you insert the buttons in a container that already exists in your HTML, use this instead: $('#myContainer').on(). It won't be noticeable, but it is best for performance.

Why not just have the listener on request, instead of inside of the loop. Also use the attr to get the data-value
$(document).ready(function(){
$('.request').click(function () {
alert($(this).attr('data-value'));
});
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.0/jquery.min.js"></script>
<button class="request box-button" data-value="18492500814">Request</button>

Try with attr method.
$(document).ready(function(){
$('.request').each(function () {
var photoID = $(this);
photoID.click(function () {
alert($(this).attr('data-value'));
});
});
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<button class="request box-button" data-value="18492500814">Request</button>

Jquery click event on button without class or id

I have this button that I can't change, nor can I edit toCashier():
<input type="button" value="Till kassan" onclick="toCashier()">
And I want to track if it's clicked and execute some javascript.
$(document).ready ( function () {
$('button[value="Till kassan"]').on('click', function(){
alert("Night button clicked");
});
});
I tried that but it doesn't seem to work. I tried various things but can't get it to work.

You have mismatched input and button, try the following :
$(document).ready ( function () {
$('input[value="Till kassan"]').on('click', function(){
alert("Night button clicked");
});
});
Or
$(document).ready ( function () {
$('input[type="button"][value="Till kassan"]').on('click', function(){
alert("Night button clicked");
});
});

button !== input
You need to use the correct selector.
$('input[value="Till kassan"]')

If you make the click with function, toCashier() function need to create :
function toCashier(){
alert("Night button clicked");
}