simulate onChange event to fire on HTML input box - javascript

I have jQuery that uses the change event from a selection box to update a input box on the form. I need the input box to fire it's change event when I update it's value.
This link on MSDN shows a way to simulate the click event. Is there a technique I can use to simulate a change event?

You can use trigger():
$('#input-id').trigger('change');

You can trigger change event handler. You can simply call it like that:
jQuery('#my_field').change();
which is a shortcut to:
jQuery('#my_field').trigger('change');
See more on the documentation of .change() (its third, attribute-less variation).

This should theoretically do it:
<input id="textinput" value="somevalue" name="somename" />
<script type="text/javascript">
function doSomethingOnInputChange(e) {
console.log('input on change');
}
$('#textinput').bind('change', doSomethingOnInputChange);
$('#textinput').trigger('change');
</script>
It binds an event handler to a custom 'change' event and then fires the event.

There are several good jQuery based answers already (though you didn't use a jQuery tag) but there's another approach that can work for you if you're binding the change event to call a function.
Say you've already bound the change event to the doSomethingOnInputChange function as in Vlad's answer...
Rather than simulating an event by triggering 'change' you can directly call doSomethingOnInputChange - that is, instead of doing:
$('#textinput').trigger('change')
your javascript just makes a call to the same function that gets called anyway when you trigger the event:
doSomethingOnInputChange( ... );
You may or may not want to pass the #textinput DOM element as a parameter in a direct call, or an event parameter (but providing your own event parameter makes this approach hardly worthwhile) -- those depend on what you need to do in the function.

Related

Jquery stop change event on manual trigger

I have bound a change event on "select box" which call when user changes select box value manually. But I want to stop change event call when we trigger change event by javascript like $(element).trigger('change').
Please help
use the off function to remove an event listener.
$(element).off('change')
Trigger method have another parameter (extraParameter ) and put your data. In handler check extraParameter to findout it is manually or with javascript code.
$(element).trigger('change',{'isTriggeredBySystem':true})
jQuery trigger

Simulate clicking a button

If I have an existing click event associated with a button, can I use code to simulate that button being pressed so the code in the click event will run? I'm asking because I want there to be certain times where the user does not have to press the button for code to be executed. I would like to press the button automatically for them in certain instances if that makes any sense.
As simple as this,
$(function() {
$('#button').trigger('click');
});
var button = document.getElementById('yourButtonIdHere');
button.click();
This will fire a click event in the button
You can trigger a click event on an element by calling the .click() function on the element. By passing no value to the function the click event will fire, as opposed to setting up a listener for the click event.
If the button has an id of "form-btn", here's what that would like:
<button id="form-btn">Submit</button>
<script type="text/javascript">
//Setup the click event
$('#form-btn').on('click', function (e) {
alert('clicked!');
});
//Call the click event
$('#form-btn').click();
</script>
This should work fine, although I usually try to use a named function when setting up my event handlers, instead of anonymous functions. By doing so, rather than triggering the event I can call the function directly.
Note that in my experience, older browsers (IE6, IE7) sometimes limit what code-triggered events can do as a safety precaution for the user.
Here's documentation on the .click() function: http://www.w3schools.com/jquery/event_click.asp
Edit 1
I forgot that jQuery also has the .trigger() function, as used in choz's answer. That will also the job quite nicely as an alternative to .click(). What's nice about .trigger() is that it can trigger standard events as well as custom events, and also allow you to pass more data in your event.
Just make a function and run the function from within the button.
Three Choices:
You can call the click event handling function directly when appropriate:
if(timeIsRightForClick){
yourClickHandler();
}
You can simulate a button click by calling the .click() method of the button.
$("#ButtonID").click()
https://api.jquery.com/click/
Same as #2, but using jQuery's trigger() function, which can be used on standard events and custom ones:
$("#ButtonID").trigger("click");
http://api.jquery.com/trigger/
Choices #2 and #3 are usually better because they will cause the event handling function to receive a reference to the click event in case it needs to use that object. Choice #1 doesn't cause an actual click event (just runs the code you tell it to) and so no event object is created or passed to the event handler.

Access all event listeners in Javascript

I want to do something like this:
function('string', function2(){})
where I leave the to user to write what he wants in the string parameter and than execute function2.
The catch is here: string is an event listener. When the user writes click, I want to call onClick(), when the user writes mouse I want to call onMouseOver and so on.
I have in mind doing something with case, but how can I access all event listeners?
You should use addEventListener.
element.addEventListener("string", function() {}, false);
However, in the case of IE <= 8, you will need to use attachEvent as it does not follow the standard:
element.attachEvent("string", function() {});
Finally, as kybernetikos mentions in his comment, you can then use a simple dictionary to map mouse to mouseover.
If you wish to fire events, you should use dispatchEvent.
If you add the event listeners using the old model (i.e. elem.onclick = function(){ /* */ };), you can use
elem['on' + event]();
Keep in mind that this only fires the event listeners, but doesn't create an event (e.g. it won't bubble).
If you won't to create a event, which fires event listeners added using addEventlistener, and bubbles, and does all things a real event does, you must
Create your event using event constructors: Event or CustomEvent
Fire it with dispatchEvent
See MDN page for more information and examples.
you can use .trigger to do this. Check out this example in jsfiddle. type "dblclick" in the input box.
http://jsfiddle.net/jspatel/Suj4H/1/
<input id="writehere"> </input>
$('#writehere').dblclick(function() {
alert ('dblclick');
});
$('#writehere').bind('keypress', function(e) {
if(e.keyCode==13){
$(this).trigger( $(this).val() );
}
});

jQuery programmatically trigger events

What all events can be triggered programmatically using jQuery? Also is there any important differences to be remembered when one is doing event triggering using jQuery Vs a natural way of it being triggered?
Every event can be programmatically fired, just use the callback-less version of it.
Example:
$('#button').click(function() { alert('event hanlder'); });
$('#button').click(); // generate the event
About your second question, there should be no difference between the native and jQuery event handlers.
One thing that is neat though is that jQuery binds this to the element that received the event, inside the callback (this doesn't happen in native event handlers):
$('#button').click(function() { alert(this); }); // here 'this' == document.getElementById('button');
Warning: the element referenced by this is not "jQuery augmented". If you want to traverse or modify it with jQuery goodness you'll have to do something like var $this = $(this);
You should know the differences between trigger and triggerHandler in jQuery.
trigger
trigger attempts to replicate the natural event as best as it can. The event handler for the event being triggered get's executed, but the default browser actions will not always be replicated exactly. For example $('a#link).trigger('click'); will execute the javascript function bound to the links click event handler, but will not redirect the browser to the href of the anchor, like a normal click would. EX: http://jsfiddle.net/AxFkD/
All the short forms of the trigger call behave exactly like trigger IE. click(), mouseup(), keydown(), etc
triggerHandler
triggerHandler prevents bubbling up ( EX. http://jsfiddle.net/LmqsS/ ), it avoids default browser behaviour and just executes the events callback, and it returns the return value of the event handler instead of a jQUery object for chaining.
You should also be aware that trigger affects all elements matched by a selector, but triggerHandler only affects the first one EX: http://jsfiddle.net/jvnyS/
You can trigger any event programmatically. But most of the events cannot be simulated as the natural event using programmatic triggers.
//to trigger a click event on a button
$("buttonSelector").trigger("click");
First, for obvious reasons, you cannot trigger the ready event.
That said, events raised by trigger() behave the same way as if they were triggered by the user. In particular, the event handlers are called in the same order.
The only difference I know of is that triggered events did not bubble up the DOM tree in older versions of jQuery (that behavior was fixed in version 1.3).

Javascript onFocus . then onClick inside function

I'm trying to make it so when an element gets focus it calls a function which then will take care of all other events - here is my code for now.
<span id="checkbox" class="checkbox" onFocus="cbHover(checkbox)"></span>
<script type="text/javascript">
function cbHover(id) {
if(document.getElementById(id).onClick) {
document.getElementById(id).style.backgroundPositionY = '-63px';
}
}
</script>
Obviously this isn't working :( So is there a way to keep the function running to listen for other events?
Thanks!
When the object is clicked, it is already focused. You can either skip the onFocus and replace it with onClick, or the other way around and remove if(document.getElementById(id).onClick) from the code, because you don't need it.
You are able to use two events: onFocus and onLostFocus. In onFocus event handler you are able to add onClick event to element:
document.getElementById(id).addEventListener('click',function_name,true);
In onLostFocus event handler you are able to remove event
document.getElementById(id).removeEventListener('click',function_name,true)
this is a bad idea even if you did get it to work you run the risk of applying multiple clicks on the same element. your best bet it to just apply the click event on dom ready I typically use jQuery
so if I where doing this in jquery i would do it like this
$(document).ready(function(){
$('.classname').click(function(){
// what to do onclick
});
});
The reason it isnt working is the parameter that is passed, should be enclosed in quotes.
It should be
onFocus="cbHover('checkbox')"
otherwise, javascript treats checkbox as a variable and tries to pass the value of the variable which is null.

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