Exploring the V8 JS engine (Part 2 of 2)

share_variable_changeable.cc

#include <v8.h>

using namespace v8;

// This is the variable we are going to share
int x = 15;

// Gets called when the value of x is requested
Handle<Value> XGetter(Local<String> property, 
                            const AccessorInfo& info) {
    // Create a new Javascript int from the
    // current value of "x"                                
    return Integer::New(x);
}

// Gets called when "x" is set to a new value
void XSetter(Local<String> property, Local<Value> value, 
                            const AccessorInfo& info) {
    // Change the value of the "x" in the C++
    // to a 32-Bit representation of the value passed
    x = value->Int32Value();
}

void CompileAndPrint(const Handle<String> source) {
    // Compile the source code.
    Handle<Script> script = Script::Compile(source);
  
    // Run the script to get the result.
    Handle<Value> result = script->Run();

    // Convert the result to an ASCII string and print it.
    String::AsciiValue ascii(result);
    printf("%s\n", *ascii);
}

int main(int argc, char* argv[]) {

  // Create a stack-allocated handle scope.
  HandleScope handle_scope;

  // Create a new ObjectTemplate
  Handle<ObjectTemplate> global_templ = ObjectTemplate::New();

  // Set the XGetter and XSetter function
  // to be called when the value of "x" is requested
  // or "x" is set to a different value.
  global_templ->SetAccessor(String::New("x"), XGetter, XSetter);

  // Create a new context.
  Persistent<Context> context = Context::New(NULL, global_templ);
  
  // Enter the created context for compiling and
  // running the hello world script. 
  context->Enter();

  // x is still equal to 15 here
  Handle<String> s1 = String::New("x;");
  CompileAndPrint(s1);
  
  // Here we change x to 250
  Handle<String> s2 = String::New("x = 250;");
  CompileAndPrint(s2);

  // We print out x in C++ to see if the value has changed
  printf("%d\n", x);
  
  // Dispose the persistent context.
  context.Dispose();
  return 0;
}

share_variable_unchangeable.cc

#include <v8.h>
#include <unistd.h>
// Include the header that contains the "getpid()" function

using namespace v8;

int main(int argc, char* argv[]) {

// Create a stack-allocated handle scope.
HandleScope handle_scope;

Handle<ObjectTemplate> global_templ = ObjectTemplate::New();
global_templ->Set(String::New("pid"), Integer::New(getpid()));

// Create a new context.
Persistent<Context> context = Context::New(NULL, global_templ);

// Enter the created context for compiling and
// running the hello world script. 
context->Enter();

// Create a string containing the JavaScript source code.
Handle<String> source = String::New("pid;");

// Compile the source code.
Handle<Script> script = Script::Compile(source);

// Run the script to get the result.
Handle<Value> result = script->Run();

// Dispose the persistent context.
context.Dispose();

// Convert the result to an ASCII string and print it.
String::AsciiValue ascii(result);
printf("%s\n", *ascii);
return 0;
}