Inline event handlers lost their arguments

seadragon · Post by **seadragon** » 2026-07-07, 11:01

Operating system: Windows 10 latest
Browser version: Pale Moon 34.3.1
32-bit or 64-bit browser?: 64-bit

The problem is the inline event handlers (like <div onclick=''>) in Pale Moon have lost access of their arguments.

From https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Attributes#event_handler_attributes:

All event handler attributes accept a string. The string will be used to synthesize a JavaScript function like function name(/*args*/) {body}, where name is the attribute's name, and body is the attribute's value. The handler receives the same parameters as its JavaScript event handler counterpart — most handlers receive only one event parameter, while onerror receives five: event, source, lineno, colno, error. This means you can, in general, use the event variable within the attribute.

A way to test the problem is as follows:

Code: Select all

<!DOCTYPE html>
<html>
<body>
<h1>HTML DOM Events</h1>
<h2>The onclick Event</h2>

<p>The onclick event triggers a function when an element is clicked on.</p>
<p>Click to trigger a function that will output "Hello World":</p>

<button onclick="myFunction()">Click me</button>

<p id="demo"></p>

<script>
function myFunction() {
  console.log(event);
  document.getElementById("demo").innerHTML = "Hello World";
}
</script>

</body>
</html>

1. Save the demo code above as an html file and open it
2. Click "Click me"

All browser other than Pale Moon will output "Hello World".

Post by **Moonchild** » 2026-07-07, 11:19

Not sure why you're seeing an issue, considering the demo code you posted works just fine. (win 10 x64/Pale Moon 34.3.1 x64)

Event logged in console:

Code: Select all

13:18:30.970 click { target: <button>, buttons: 0, clientX: 22, clientY: 214, layerX: 22, layerY: 214 } 1 test.html:15:11

I found the report peculiar since we haven't touched those handlers for quite a while... and I'd also expect there to be a lot of breakage reports if it was broken

seadragon · Post by **seadragon** » 2026-07-07, 11:23

Thank you for the reply. It's strange... Let me reinstall Pale Moon and see if the problem vanished. If not, I will provide more troubleshooting information.

Post by **jobbautista9** » 2026-07-07, 11:26

dom.window.event.enabled in about:config needs to be true for the testcase to work.

seadragon · Post by **seadragon** » 2026-07-07, 11:30

jobbautista9 wrote: ↑
2026-07-07, 11:26
dom.window.event.enabled in about:config needs to be true for the testcase to work.

It is the problem. I'm not sure why the default value is false

Post by **jobbautista9** » 2026-07-07, 11:35

seadragon wrote: ↑
2026-07-07, 11:30
I'm not sure why the default value is false

Because it is a deprecated property (it was a non-standard introduced first by IE iirc before it got written into the living standard for DOM when Blink and WebKit refused to remove support for it due to how widespread its usage is) which we were trying to discourage using (and still are as you can see with it being disabled by default). Even Mozilla which introduced support for window.event very late (version 66) made it clear in their MDN that it is not recommended to use it: https://developer.mozilla.org/en-US/doc ... ndow/event

seadragon · Post by **seadragon** » 2026-07-07, 11:44

My feeling is that this feature has some real use cases in the wild and disabling it by default will cause some real web compatibility issues (I found this problem while testing my own web project). Nevertheless, as this kind of default setting is by design, I have no objection to that.

To be absolutely sure that this is the cause, I would like to know if Moonchild has this flag on so that the demo works?

Post by **vannilla** » 2026-07-07, 12:17

To make the event handler work without relying on the deprecated global event and the about:config flag being toggled, it should be written like so:

Code: Select all

function handler(event) {
  console.log(event);
}

and used like this:

Code: Select all

<button onclick="handler(event)">Click me</button>

Or you can write the function body directly inside the string:

Code: Select all

<button onclick="targetelement.innerHTML = 'Hello world'">Click me</button>

Or use addEventListener if you can, since its behaviour is less confusing.

seadragon · Post by **seadragon** » 2026-07-07, 12:42

Thank you very much. I always thought that I was using the event passed into the event handler, while actually I was using the deprecated window.event.

Pale Moon helps me understand how to write in a more standard way, and I am grateful for that.

Post by **Moonchild** » 2026-07-07, 14:46

Ah yes I missed that because my current profile has it flipped on, and I didn't look too closely at the code since it worked and on* stuff is mature and stable. Sorry about that.

Indeed, the proper way to use this is to pass the event into the event handler. The global event is fragile and may not always have the expected value (in any browser, not just us).

Pale Moon forum

Inline event handlers lost their arguments

Inline event handlers lost their arguments

Re: Inline event handlers lost their arguments

Re: Inline event handlers lost their arguments

Re: Inline event handlers lost their arguments

Re: Inline event handlers lost their arguments

Re: Inline event handlers lost their arguments

Re: Inline event handlers lost their arguments

Re: Inline event handlers lost their arguments

Re: Inline event handlers lost their arguments

Re: Inline event handlers lost their arguments