Does someone know how I could look up local variables in a nested function call from C++? Consider the following example:
// e.g. a global variable in the browser
var global = "global_value";
function foo(){
var global = "local_value";
myCppFunction("global", global);
}
foo();
My question now is how in the implementation of myCppFunction
I could access the function local variable "global" (NOT value, this would be given by the 2nd parameter) from 'foo'?
Handle<Value> MyCppFunction(const Arguments& args){
Local<String> varName = args[0]->ToString();
Local<String> varValue = args[1]->ToString(); // this holds "local_value"
// how to access the variable "global" in the scope of 'foo' ?
}
I managed to find it out by myself. See the example below for how to find the value on the stack (and also replace it - here by the example of a string variable).
Two remarks beforehand:
sfl.FindJavaScriptFrame(0)
yields the desired stack frame - but, as it works independently of the calling depth, I suspect the stack frame indexed by 0 to always be the immediate caller's frame (in my case I know that I want exactly that).And the code:
// Prepare identification of the variable,assuming varName as in the question
// More convenient conversions would be appreciated, at least by me
Local<String> varName = args[0]->ToString();
std::string varStr = *String::AsciiValue(varName);
// I'm using 'namespace i = internal;' (within v8-namespace)
i::Vector<const char> tmpVar(varStr.data(), varStr.length());
i::Handle<i::String> varIStr = i::Isolate::Current()->factory()->NewStringFromAscii(tmpVar, i::TENURED);
// Now hunt down the stack frame of interest, be sure to consider my remarks above
i::StackFrameLocator sfl;
// Comment from the code: The caller must guarantee that such a frame exists.
i::JavaScriptFrame* jsf = sfl.FindJavaScriptFrame(0);
// create some replacement
i::Vector<const char> tmp("there you go", 12);
i::Handle<i::String> insert = i::Isolate::Current()->factory()->NewStringFromAscii(tmp, i::TENURED);
i::Object* insertObj = insert->ToObjectChecked();
// by the help of JavaScriptFrame::Print I came up with this:
i::Object* fun = jsf->function();
if (fun->IsJSFunction()){
i::Handle<i::ScopeInfo> scope_info(i::ScopeInfo::Empty());
i::Handle<i::SharedFunctionInfo> shared((i::JSFunction::cast(fun))->shared());
scope_info = i::Handle<i::ScopeInfo>(shared->scope_info());
i::Object* script_obj = shared->script();
if (script_obj->IsScript()) {
int stack_locals_count = scope_info->StackLocalCount();
for (int i = 0; i < stack_locals_count; i++) {
if (scope_info->StackLocalName(i)->Equals(*varIStr)){
// replace the value on the stack
jsf->SetExpression(i,insertObj);
}
}
}
}