Order of Event Handler Execution

Order of event handler execution

Currently, they are executed in the order they are registered. However, this is an implementation detail, and I would not rely on this behavior staying the same in future versions, since it is not required by specifications.

what if I need to execute event handlers in certain order?

I would not rely on the internal implementation to ensure that the handlers get called in a specific order.

If the handlers can't know about each other but you need them to run in a certain order I would create a "parent" handler that calls the other two handlers in the correct order.

Order of execution of functions bound to an event in Javascript

Event handlers are always called in the order in which they were registered.

Once registered, you cannot insert additional handlers ahead of them[*].

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[*] unless you are some how able to obtain a list of all the handlers, and their EventListener objects, and call removeEventListener to remove them, insert your own, and then reinsert the originals. In practise this is likely to be impossible.

Javascript event handler order

Normally you'd have the Save event handler call Validate() which will return true if everything is fine and ready to be saved.

function onSaved() {
  if (!validate()) {
    // set class
    return;
  }

  // do the save
}

C# Event execution order (Unity3D game)

Yes, synchronous event handlers as shown in the post are guaranteed to finish after executing sequentially (in some order - Order of event handler execution) before execution returns back to code that triggered event.

So your code is guaranteed to print A,B,C.

More links: are C# events synchronous?, making event asynchronous - Should I avoid 'async void' event handlers? , awaiting for asynchronous events - Asynchronous events in C#.

JavaScript event handlers execution order

The alerts will be executed in order - 1 and then 2. This is because click event is synchronous (see here) - when .click() is issued the handler will be run immediately (look at the last paragraph here). So this code:

document.getElementById('e1').addEventListener('click', function(){alert('1');}, false);
document.getElementById('e2').addEventListener('click', function(){alert('2');}, false);
document.getElementById('e1').click();
document.getElementById('e2').click();
alert('3');

will produce the same result as

alert('1');
alert('2');
alert('3');

Event Handling order

Events bubble "up" the DOM tree, so if you've got handlers for an element and its parent, the child element handler will be called first.

If you register more than one handler for an event on a single DOM element (like, more than one "click" handler for a single button), then the handlers are called in the order that they were attached to the element.

Your handlers can do a few things to change what happens after they're done:

• With the passed-in event parameter, call event.preventDefault() to keep any "native" action from happening
• call event.stopPropagation() to keep the event from bubbling up the DOM tree
• return false from the handler, to both stop propagation and prevent default

Note that for some input elements (checkboxes, radio buttons), the handling is a little weird. When your handler is called, the browser will have already set the checkbox "checked" value to the opposite of its former value. That is, if you have a checkbox that is not checked, then a "click" handler will notice that the "checked" attribute will be set to "true" when it is called (after the user clicks). However, if the handler returns false, the checkbox value will actually NOT be changed by the click, and it will remain un-checked. So it's like the browser does half of the "native" action (toggling the element "checked" attribute) before calling the handler, but then only really updates the element if the handler does not return false (or call "preventDefault()" on the event object).

javascript order of execution of event handlers

As best I can tell through empirical testing, the click event handlers are executed in the order they were attached to the object. The first one attached is the first one to execute.

Here's a test bed that I ran in Chrome, Firefox, IE9 and Safari and they all executed the event handlers in the order they were initially attached.

Working test bed: http://jsfiddle.net/jfriend00/yTYxV/

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