Question

overide a function and call the original

Asked by: aperdon

I have to add some functionality (website stats) to a website. And to do this I have to "break-in" into a javascript-method called "validateInput". I don't want to change this code and prefer a solution like this

function validateInput() {
   call original validateInput();
   log website stats
}

How can I do this?

So far I renamed the original function to doValidateInput, but I prefer not changing this code.

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Asked On
2009-07-21 at 08:26:51ID24587699
Topic

JavaScript

Participating Experts
3
Points
125
Comments
8

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Answers

 

by: dhiraj05Posted on 2009-07-21 at 09:09:23ID: 24906246

this cannot be done... you must change the name of one of the functions... javascript cannot refer two different functions with same name.

 

by: TeggertPosted on 2009-07-21 at 09:15:02ID: 24906321

Can you show us the actual code? Might be able to work something out for you if we can get a look at it.

 

by: HonorGodPosted on 2009-07-21 at 11:13:09ID: 24907594

The only way to do this is something like:

var oldValidateInput = validateInput;
 
function validateInput() {
  if ( oldValidateInput ) {
   oldValidateInput();
  }
  ... log website stats
}

                                              
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Select allOpen in new window

 

by: HonorGodPosted on 2009-07-21 at 11:13:45ID: 24907599

I do this all the time with "window.onload" to nest multiple onload routines.

 

by: aperdonPosted on 2009-07-21 at 12:30:37ID: 24908355

@HonorGod.

Thanx, I will test this tomorrow. But I am almost sure it will work :-)

However, it would be nice if Javascript would provide prefixes for included javascripts (like namespaces in xml). In fact I hoped there would be already a syntax for this, like <module>.<function>

Btw. For window.onload I use prototype.js. (Event.observe)
check http://www.prototypejs.org/api/event/observe

 

by: HonorGodPosted on 2009-07-21 at 13:07:29ID: 24908772

I understand.  jQuery and prototype and some other frameworks are things that I have not yet had the time to pursue... in my copious spare time.  :-)

 

by: aperdonPosted on 2009-08-25 at 13:19:04ID: 25181801

I forgot to remark that it wont always work. If the old-function is within the same <script>-tag it wont work, and the result will be a stack-overflow because the variable oldValidateInput will point to the new validateInput.

 

by: HonorGodPosted on 2009-08-25 at 20:25:32ID: 25184213

Thanks for the grade & points.

Good luck & have a great day.

20120131-EE-VQP-002

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