Subj : Re: recommendation for XML Events
To   : Aaron Reed
From : Brendan Eich
Date : Fri May 14 2004 04:16 pm

Aaron Reed wrote:
> Hey,
> 
> In the course of trying to implement XML Events (bug 164482) we're 
> trying to make <script> tags basically execute like JavaScript 
> functions.  So that you could have something like:
> 
> ....
> <script id="popper" type="application/x-javascript" declare="declare">
>    alert("popper action hit");
> </script>
> 
> <a href="doc.html" ev:event="activate" ev:handler="#popper"> The 
> Document </a>
> ....
> 
> So if you click on the link "The Document", you would get a javascript 
> alert saying, "popper action hit".
> 
> So what we have done so far is pretty much just add a method to 
> nsHTMLScriptElement that gets called when the script needs to execute. 
> This method gets the JS code from the contents of the <script> tag, call 
> scriptContext->CompileFunction to get a function object, then call 
> scriptContext->CallEventHandler passing in the functionObject and the 
> arguments.


This is a fine experiment to get started, but not the patch to submit 
for checkin, as you allow below.

We need to get this going for XML languages that have <script> tags too.


> This code works just fine.  No problems.  However, we recognize that 
> this could be really inefficient, especially if the handler is some kind 
> of mousemove handler or a handler attached to a bunch of different 
> elements.  Compiling and executing the script on every invocation must 
> be expensive.  So I'm guessing that we need some way to cache the 
> resulting compiled code (I assume compiling the code is the most 
> inefficient part) and/or keeping around the functionObject.  Is this 
> kind of thing already done somewhere in Mozilla that we can use as an 
> example?  Any "gotchas" to look out for?


All event handlers are currently compiled once, called N times, N >= 0. 
  In fact we lazily compile on first call, so N > 0.  See 
http://lxr.mozilla.org/mozilla/ident?i=CompileEventHandler, note that 
nsIScriptContext and nsIScriptEventHandlerOwner both have a method of 
this name.  See especially 
http://lxr.mozilla.org/mozilla/search?string=mHandlerIsString.

This is really a m.dom question, since you should not be using jsapi.h 
directly, rather nsIScriptContext and friends.

/be

.