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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');
}

How to corectly bind events in a loop

On a page I have couple of divs, that look like this:
<div class="product-input">
<input type="hidden" class="hidden-input">
<input type="text">
<button class="remove">X</button>
</div>
I'm trying to bind an event to that remove button with this code (simplified):
$('.product-input').each(function() {
product = $(this);
product_field = product.find('.hidden-input');
product.on('click', '.remove', function(event) {
product_field.val(null);
});
});
It works perfectly when there is only one "product-input" div. When there is more of them, all remove buttons remove value from the hidden field from the last product-input div.
https://jsfiddle.net/ryzr40yh/
Can somebody help me finding the bug?

You dont need to iterate over the element for binding the same event. you can rather bind the event to all at once:
$('.product-input').on('click', '.remove', function(event) {
$(this).prevAll('.hidden-input').val("");
});
If the remove buttons are not added dynamically, you will not need event delegation:
$('.remove').click(function(event) {
$(this).prevAll('.hidden-input').val("");
});
Working Demo

You need to declare product and product_field as local variables, now they are global variables. So whichever button is clicked inside the click handler product_field will refer to the last input element.
$('.product-input').each(function() {
var product = $(this);
var product_field = product.find('.hidden-input');
product.on('click', '.remove', function(event) {
product_field.val(null);
});
});
Demo: Fiddle
But you can simplify it without using a loop as below using the siblings relationship between the clicked button and the input field
$('.product-input .remove').click(function () {
$(this).siblings('.hidden-input').val('')
})
Demo: Fiddle

javascript onclick change onclick to new function

I need to be able to change the onclick event of an id so that once it has been clicked once it executes a function which changes the onclick event
Here is my code:
Javascript:
function showSearchBar()
{
document.getElementById('search_form').style.display="inline";
document.getElementById('searchForm_arrow').onclick='hideSearchBar()';
}
function hideSearchBar()
{
document.getElementById('search_form').style.display="none";
document.getElementById('searchForm_arrow').onclick='showSearchBar()';
}
and here is the HTML:
<!-- Search bar -->
<div class='search_bar'>
<img id='searchForm_arrow' src="images/icon_arrow_right.png" alt=">" title="Expand" width="10px" height="10px" onclick='showSearchBar()' />
<form id='search_form' method='POST' action='search.php'>
<input type="text" name='search_query' placeholder="Search" required>
<input type='image' src='images/icon_search.png' style='width:20px; height:20px;' alt='S' >
</form>
</div>
Thanks

Change your code in two places to reference the new functions directly, like:
document.getElementById('searchForm_arrow').onclick=hideSearchBar;

Can you try this,
function showSearchBar()
{
if(document.getElementById('search_form').style.display=='none'){
document.getElementById('search_form').style.display="inline";
}else{
document.getElementById('search_form').style.display="none";
}
}

You were nearly right. You are settingthe onclick to a string rather than a function. Try:
in showSearchBar()
document.getElementById('searchForm_arrow').onclick=hideSearchBar;
in hideSearchBar()
document.getElementById('searchForm_arrow').onclick=showSearchBar;

You do not need to create two function.
Just create one function and using if condition you can show and hide the form tag..
function showSearchBar()
{
if(document.getElementById('search_form').style.display=='none'){
document.getElementById('search_form').style.display=''; // no need to set inline
}else{
document.getElementById('search_form').style.display='none';
}
}

function searchBar(){
var x = document.getElementById('search_form').style.display;
x = (x == 'inline') ? 'none' : 'inline';
}
You can wrap up both functions into one by adding a check to the current condition of the element and applying your style based on that condition. Doesn't actually change the function but doesn't need to as there is now only one functon performing both actions.

With javascript you can check and perform opration
function SearchBarevent()
{
if(document.getElementById('search_form').style.display=='none'){
document.getElementById('search_form').style.display="inline";
}else{
document.getElementById('search_form').style.display="none";
}
}
or if you may go for jquery there is better solution toogle
Like:
$("#button_id").click(function(){
$( "#search_form" ).toggle( showOrHide );
});
Fiddle is example

Here is an option that uses jQuery:
$('#searchForm_arrow').click(function() {
$('#search_form').slideToggle();
});
http://jsfiddle.net/PuTq9/

Hooking events with .on() with JQUERY

I want to hook events with the .on() method. The problem is I don't know how to get the object reference of the element on which the event take place. Maybe it's a midunderstanding of how the method really works... but I hope you can help.
Here's what I want to do:
When a file is selected, I want the path to be displayed in a div
<div class="wrapper">
<input type="file" class="finput" />
<div class="fpath">No file!</div>
</div>
Here's my script
$(document).ready(function() {
$this = $(this);
$this.on("change", ".finput", {}, function() {
var path = $(this).val()
$(this).parents().children(".fpath").html(path.split("\\").pop());
});
});
Something like that but that way it doesn't work.

Like this
$(document).ready(function() {
$('.finput').on("change", function() {
var path = $(this).val()
$(this).parents().children(".fpath").html(path.split("\\").pop());
});
});

Do you need to use on()? I'm not sure what you are trying to do exactly.
$("#wrapper").on("change", ".finput", function(event){
var path = $(this).val()
$(this).parents().children(".fpath").html(path.split("\\").pop());
});
I haven't tested your code, but you need to attach the on() to the wrapper.
Can you just use change()?
$('.finput').change(function() {
var path = $(this).val()
$(this).parents().children(".fpath").html(path.split("\\").pop());
});

This should help. If you want to see when a file input changes, bind the event to it
$("input[type='file']").on("change", function(e){
var path = $(this).val();
})

Try:
$(document).ready(function() {
$('body').on('change','input.finput', function() {
var path = $(this).val()
$(this).parent().children(".fpath").html(path.split("\\").pop());
});
});

$(document).on("change", ".finput", function() {
$(".fpath").html(this.value.split("\\").pop());
});
This is a delegated event handler, meaning the .finput element has been inserted dynamically so we need to delegate the listening to a parent element.
If the .finput element is not inserted with Ajax and is present on page load, you should use something like this instead:
$(".finput").on("change", function() {
$(".fpath").html(this.value.split("\\").pop());
});

Best way to modify an element that is not yet created

I have an <input> field in my web page, and I want to add a particular method on it, let say fooBar().
Here is what I do:
<input id="xxx" .../>
<script type="text/javascript">
$("xxx").fooBar = function() { ... };
</script>
This works well. However, for some reasons I will not detail here (in fact the HTML is generated by JSF components), the <script> will be declared before the <input> tag.
So in others words, I will have that in my HTML:
<script type="text/javascript">
$("xxx").fooBar = function() { ... };
</script>
<input id="xxx" .../>
So of course this code will not work correctly, as the script will try to get ($("xxx")) and modify an element that does not exist yet.
If I want to stick on the exact order of these two tags, what is the best way to accomplish what I want?
Edit
In my case, $ refers to prototype, but I am also using jQuery in my application. And I must be compatible with IE6 :o(

You need to run your script after the document is loaded. With jQuery you'd do that with:
$(document).ready(function () {
//do stuff here
});
I can't tell which library you're using here, but they all have an equivalent of jQuery's document ready.
Here's the prototype equivalent:
document.observe("dom:loaded", function() {
// do stuff
});

Try putting your code in load event:
$(window).load(function(){
$("#xxx").fooBar = function() { ... };
});

If the code has to be directly before the input, you can check if it has loaded after a certain period of time.
<script type="text/javascript">
//Sets up a function to execute once the input is loaded
f = function ()
{
//Checks if 'xxx' exists (may vary between frameworks)
if ($("xxx") !== undefined)
{
$("xxx").fooBar = function() { ... };
//Escapes the timer function, preventing it from running again
return true;
}
//If still not loaded check again in half a second (0.5s or 500ms)
setTimeout(f,500);
return false;
}
f();//Initialize the timer function
</script>
<input id="xxx" .../>

Instead of adding a method to the dom node, why not make it a separate function, so instead of
$("xxx").fooBar = function() {
doStuff(this);
};
you would have something like
function xxx_fooBar () {
var me = document.getElementById('xxx');
doStuff(me);
};
Another suggestion: If you can add attributes to the <input> element, you could do something like this...
<script>
function xxx_init (e) {
e.fooBar = function () {
doStuff(this);
};
}
</script>
<input onload="xxx_init(this)" id="xxx" .../>
Or you could do as others suggest and attach the scripts to the window.onload event.