Hi Zhe.
I'm developing an application which uses webkit's JavaScriptCore
and a customized global object (by providing a special class when
creating the context). My customized global object provides some
built-in properties that can be accessed by javascript code. Now, I
want to support a special behavior: allows javascript code to
override a built-in property of global object by using variable
declaraction statement. For example, assuming the global object has
a built-in property, named "foo", a "var foo;" statement shall
create a javascript variable, named "foo" and the original built-in
"foo" shall be overrid by this new javascript variable. But if there
is no "var foo;" statement, the built-in foo shall be able to get
and set from javascript code.
Now the problem is, current JavaScriptCore's C API (especially those
HasProperty, GetProperty, SetProperty callbacks of a class
definition) can't distinguish variable delcaration statement and
variable assigment statement. I checked SpiderMonkey's API and found
it can distinguish such things by providing a flag when calling
ResolveProperty callback.
I'm surprised to hear that SpiderMonkey's property setting API
includes a flag distinguishing var declarations from other kinds of
property setting. Internet Explorer supports shadowing global
properties with var declarations, but Firefox does not. (Perhaps
you're thinking of the SpiderMonkey flag to distinguish "x = y" syntax
from "this.x = y" syntax, which is slightly different.)
It may not be my place, but I would discourage you from giving var
declarations a special behavior, distinct from their behavior on the
web. Much of the value of JavaScript derives from the fact that so
many programmers understand how it works, due to their experience with
the web.
Do you have any idea on this issue? How can I implement such
behavior based on current API?
There is no API in JavaScriptCore for distinguishing between "var" and
other property setting. I'm not sure how you would implement that.
Geoff
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