Thanks, Stephan.
It looks like what you're doing will execute the code and set "this"
to the object in question.
However, what I'd really like to do is execute code and set a given
object as the global scope. Here's an example with some code:
var code = "var foo = 'bar';";
var obj = { foo : "baz" };
evalcx( code, obj ); // execute code using "obj" as the global object
print( obj.foo ); // prints "bar"
Unless I'm misreading your example, what you're describing will work
in this case:
var code = "this.foo = 'bar';";
var obj = { foo : "baz" };
But, I can already do that from JS like so:
(new Function(code)).call(obj);
If I could eval code in an arbitrary global scope within Javascript,
which did not have any access to the global scope, then it would be
possible to implement a capability-based security model.
Also, it would make it possible to load and execute many different
scripts in a row without having to "clean up" the globals that each
one might create. After being evaluated, the temporary global scope
could be discarded, and would be garbage collected normally.
For example, let's say you have a fastcgi handler written in
Javascript, which reads and evals the SCRIPT_FILENAME file. The
problem is that, since the evaled code shares a global scope with the
fcgi handler, it also shares a global scope with *every other script
loaded by that handler.* That means that every global variable is
persistent in memory, and only gets garbage collected when you restart
the server. Not ideal! :)
--
Isaac Z. Schlueter
On Mar 1, 5:06 pm, Stephan Beal <[email protected]> wrote:
> On Mar 2, 1:34 am, "Isaac Z. Schlueter" <[email protected]> wrote:
>
> > I'm trying to write a function that will execute a bit of Javascript
> > within an arbitrary global scope. Something like the "evalcx"
> > function in the Spidermonkey shell.
>
> > I've got a function defined and exposed to the Javascript that takes
> > an object as an argument, and stores it as a Handle<Object>. However,
> > in order to create a new execution context, I need a
> > Handle<ObjectTemplate>.
>
> Do you need a new Context, or just an object to eval the code in? If
> you just need an Object to execute the code in...
>
> They way i ended up doing this was getting the 'eval' function from my
> local object, then using Call() on that Function object:
>
> TryCatch tryer;
> Local<Value> rv;
> Local<Function> eval = Function::Cast( *(db->jsobj->Get(String::New
> ("eval"))) );
> // ^^^^^ db->jsobj is my context object
> for( int i = 0; i < argc; ++i )
> {
> char const * cp = reinterpret_cast<char const *>
> ( sqlite3_value_text( argv[i] ) );
> if( ! cp || !*cp ) continue;
> Local<Value> arg = String::New( cp, sqlite3_value_bytes( argv
> [i] ) );
> rv = eval->Call( db->jsobj, 1, &arg );
> // ^^^^ that will, in theory, eval the code in the context of db->jsobj
>
> if( rv.IsEmpty() )
> {
> std::string err( CastFromJS<std::string>( tryer.Exception() )
> );
> sqlite3_result_text( context, err.c_str(),
> static_cast<int>(err.size
> ()), SQLITE_TRANSIENT );
> return;
> }
> }
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