NodeJS Lambda function execution flow

handler.js

const doSomething = () => {
    console.log('Do Something Executed');
}

// no callback invoked
module.exports.handler = function () {
  // Lambda finishes AFTER `doSomething()` is invoked
  setTimeout(() => doSomething(), 1000);
};

// callback invoked
module.exports.handler = function (event, context, callback) {
  // Lambda finishes AFTER `doSomething()` is invoked
  setTimeout(() => doSomething(), 1000);
  callback(null, "Hello World!");
};

// callback invoked, context.callbackWaitsForEmptyEventLoop = false
module.exports.handler = function (event, context, callback) {
  // Lambda finishes BEFORE `doSomething()` is invoked
  context.callbackWaitsForEmptyEventLoop = false;
  setTimeout(() => doSomething(), 2000);
  setTimeout(() => callback(null, "Hello World!"), 1000);
};

// async/await
module.exports.handler = async function () {
  // Lambda finishes BEFORE `doSomething()` is invoked
  setTimeout(() => doSomething(), 1000);
  return "Hello World!";
};

// Promise
module.exports.handler = function () {
  // Lambda finishes BEFORE `doSomething()` is invoked
  setTimeout(() => doSomething(), 1000);
  return Promise.resolve("Hello World!");
};

Referenced from https://sequelize.org/docs/v7/other-topics/aws-lambda/