Hello World with V8 Engine Link to heading

There are two popular javascript engines out there: V8 and Javascript Core. The V8 engine is developed by Google and is powering Chrome…

There are two popular javascript engines out there: V8 and Javascript Core. The V8 engine is developed by Google and is powering Chrome browser as well as node and deno. The Javascript Core engine is developed by Apple is powering Safari browser and bun. Today, let’s compile and run a simple hello world app that embeds Javascript code with the V8 engine into C++ code.

I was only able to run on Fedora and macOS, not Ubuntu.

First, you will need v8 engine library.

# fedora
sudo dnf install v8-devel
# macOS
brew install v8

Then, let’s grab code from official V8 project

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "include/libplatform/libplatform.h"
#include "include/v8-context.h"
#include "include/v8-initialization.h"
#include "include/v8-isolate.h"
#include "include/v8-local-handle.h"
#include "include/v8-primitive.h"
#include "include/v8-script.h"
int main(int argc, char* argv[]) {
  // Initialize V8.
  v8::V8::InitializeICUDefaultLocation(argv[0]);
  v8::V8::InitializeExternalStartupData(argv[0]);
  std::unique_ptr<v8::Platform> platform = v8::platform::NewDefaultPlatform();
  v8::V8::InitializePlatform(platform.get());
  v8::V8::Initialize();
  // Create a new Isolate and make it the current one.
  v8::Isolate::CreateParams create_params;
  create_params.array_buffer_allocator =
      v8::ArrayBuffer::Allocator::NewDefaultAllocator();
  v8::Isolate* isolate = v8::Isolate::New(create_params);
  {
    v8::Isolate::Scope isolate_scope(isolate);
    // Create a stack-allocated handle scope.
    v8::HandleScope handle_scope(isolate);
    // Create a new context.
    v8::Local<v8::Context> context = v8::Context::New(isolate);
    // Enter the context for compiling and running the hello world script.
    v8::Context::Scope context_scope(context);
    {
      // Create a string containing the JavaScript source code.
      v8::Local<v8::String> source =
          v8::String::NewFromUtf8Literal(isolate, "'Hello' + ', World!'");
      // Compile the source code.
      v8::Local<v8::Script> script =
          v8::Script::Compile(context, source).ToLocalChecked();
      // Run the script to get the result.
      v8::Local<v8::Value> result = script->Run(context).ToLocalChecked();
      // Convert the result to an UTF8 string and print it.
      v8::String::Utf8Value utf8(isolate, result);
      printf("%s\n", *utf8);
    }
    {
      // Use the JavaScript API to generate a WebAssembly module.
      //
      // |bytes| contains the binary format for the following module:
      //
      //     (func (export "add") (param i32 i32) (result i32)
      //       get_local 0
      //       get_local 1
      //       i32.add)
      //
      const char csource[] = R"(
        let bytes = new Uint8Array([
          0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x01, 0x07, 0x01,
          0x60, 0x02, 0x7f, 0x7f, 0x01, 0x7f, 0x03, 0x02, 0x01, 0x00, 0x07,
          0x07, 0x01, 0x03, 0x61, 0x64, 0x64, 0x00, 0x00, 0x0a, 0x09, 0x01,
          0x07, 0x00, 0x20, 0x00, 0x20, 0x01, 0x6a, 0x0b
        ]);
        let module = new WebAssembly.Module(bytes);
        let instance = new WebAssembly.Instance(module);
        instance.exports.add(3, 4);
      )";
      // Create a string containing the JavaScript source code.
      v8::Local<v8::String> source =
          v8::String::NewFromUtf8Literal(isolate, csource);
      // Compile the source code.
      v8::Local<v8::Script> script =
          v8::Script::Compile(context, source).ToLocalChecked();
      // Run the script to get the result.
      v8::Local<v8::Value> result = script->Run(context).ToLocalChecked();
      // Convert the result to a uint32 and print it.
      uint32_t number = result->Uint32Value(context).ToChecked();
      printf("3 + 4 = %u\n", number);
    }
  }
  // Dispose the isolate and tear down V8.
  isolate->Dispose();
  v8::V8::Dispose();
  v8::V8::DisposePlatform();
  delete create_params.array_buffer_allocator;
  return 0;
}

This official hello-world source code is intended to work with V8 engine built from source code. Hence, we need to modify is a bit. In particular, we will need to remove all include/ from its include paths.

--- before
+++ after
@@ -1,13 +1,13 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include "include/libplatform/libplatform.h"
-#include "include/v8-context.h"
-#include "include/v8-initialization.h"
-#include "include/v8-isolate.h"
-#include "include/v8-local-handle.h"
-#include "include/v8-primitive.h"
-#include "include/v8-script.h"
+#include "libplatform/libplatform.h"
+#include "v8-context.h"
+#include "v8-initialization.h"
+#include "v8-isolate.h"
+#include "v8-local-handle.h"
+#include "v8-primitive.h"
+#include "v8-script.h"
 int main(int argc, char* argv[]) {
   // Initialize V8.
   v8::V8::InitializeICUDefaultLocation(argv[0]);

Now, we are ready to compile!

# fedora
g++ -I/usr/include/v8 -o hello-world hello-world.cc -lv8 -lv8_libplatform -pthread
# macOS
g++ -I $(brew --prefix v8)/include -std=c++20 -o hello-world hello-world.cc  -L$(brew --prefix v8)/lib -lv8 -lv8_libplatform -DV8_COMPRESS_POINTERS -DV8_ENABLE_SANDBOX

# run!
./hello-world

If successful, you should see

Hello, World!
3 + 4 = 7