Node.js v16.20.2 documentation

Table of contents

C++ embedder API#

Node.js provides a number of C++ APIs that can be used to execute JavaScript in a Node.js environment from other C++ software.

The documentation for these APIs can be found in src/node.h in the Node.js source tree. In addition to the APIs exposed by Node.js, some required concepts are provided by the V8 embedder API.

Because using Node.js as an embedded library is different from writing code that is executed by Node.js, breaking changes do not follow typical Node.js deprecation policy and may occur on each semver-major release without prior warning.

Example embedding application#

The following sections will provide an overview over how to use these APIs to create an application from scratch that will perform the equivalent of node -e <code>, i.e. that will take a piece of JavaScript and run it in a Node.js-specific environment.

The full code can be found in the Node.js source tree.

Setting up per-process state#

Node.js requires some per-process state management in order to run:

  • Arguments parsing for Node.js CLI options,
  • V8 per-process requirements, such as a v8::Platform instance.

The following example shows how these can be set up. Some class names are from the node and v8 C++ namespaces, respectively.

int main(int argc, char** argv) {
  argv = uv_setup_args(argc, argv);
  std::vector<std::string> args(argv, argv + argc);
  std::vector<std::string> exec_args;
  std::vector<std::string> errors;
  // Parse Node.js CLI options, and print any errors that have occurred while
  // trying to parse them.
  int exit_code = node::InitializeNodeWithArgs(&args, &exec_args, &errors);
  for (const std::string& error : errors)
    fprintf(stderr, "%s: %s\n", args[0].c_str(), error.c_str());
  if (exit_code != 0) {
    return exit_code;
  }

  // Create a v8::Platform instance. `MultiIsolatePlatform::Create()` is a way
  // to create a v8::Platform instance that Node.js can use when creating
  // Worker threads. When no `MultiIsolatePlatform` instance is present,
  // Worker threads are disabled.
  std::unique_ptr<MultiIsolatePlatform> platform =
      MultiIsolatePlatform::Create(4);
  V8::InitializePlatform(platform.get());
  V8::Initialize();

  // See below for the contents of this function.
  int ret = RunNodeInstance(platform.get(), args, exec_args);

  V8::Dispose();
  V8::ShutdownPlatform();
  return