Comments on: Getting Rid of the "handler.call: handler undefined" Error

By: Pums

Pums — Sat, 11 Jul 2009 10:09:30 +0000

document.observe(‘dom:loaded’, function(){test(‘hi’)});

Seems to work ok when parameters are needed in the callback

By: juanjo

juanjo — Mon, 06 Jul 2009 10:15:24 +0000

I have the same question. How can I pass a parameter to the callback function? If i do, the handler becomes undefined.

Thanks in advance!

By: Bruno Lacerda

Bruno Lacerda — Tue, 09 Jun 2009 12:03:11 +0000

Hi Daniel Convissor.
And if the calback function needs a parameter to be executed?
How can I pass this parameter to the calback or in this case it’s not necessary?

By: Daniel Convissor

Daniel Convissor — Tue, 10 Mar 2009 16:22:56 +0000

The problem arises when the handler parameter to Event.observe is undefined. The likely cause of your error is the following.

// Wrong. Passing result of callback function.
Event.observe(window, “load”, the_callback());

In the example above, the_callback() is being executed as you are making the Event.observe() call. That means the _result_ of the_callback() is being passed as the “handler” parameter of Event.observe().

// Correct. Passing name of callback function.
Event.observe(window, “load”, the_callback);

In this case, you are passing the _name_ of the function to the “handler” parameter of Event.observe().

By: Tyche

Tyche — Sat, 07 Mar 2009 16:19:49 +0000

Thank you for publishing this fix , I’m glad you were as annoyed as I was with this error

By: Srikant

Srikant — Fri, 06 Mar 2009 18:49:55 +0000

Thanks for the solution.
It takes care of error.

By: Quleczka

Quleczka — Sun, 01 Mar 2009 13:05:12 +0000

thanks for info my first thought was it is me doing something wrong with prototype Event.observe

By: BugFix

BugFix — Sun, 08 Feb 2009 06:27:16 +0000

Thanxs a lot – it helped!

By: Sander

Sander — Tue, 27 Jan 2009 23:46:42 +0000

Thank you! This indeed prevents the ‘handler is undefined’ error from showing up. I use Prototype a lot to observe dom:loaded and never understood where this error came from.