Node: Up and Running

Processes

Although Node abstracts a lot of things from the operating system, you are still running in an operating system and may want to interact more directly with it. Node allows you to interact with system processes that already exist, as well as create new child processes to do work of various kinds. Although Node itself is generally a “fat” thread with a single event loop, you are free to start other processes (threads) to do work outside of the event loop.

process Module

The process module enables you to get information about and change the settings of the current Node process. Unlike most modules, the process module is global and is always available as the variable process.

process events

process is an instance of EventEmitter, so it provides events based on systems calls to the Node process. The exit event provides a final hook before the Node process exits (see Example 5-14). Importantly, the event loop will not run after the exit event, so only code without callbacks will be executed.

Example 5-14. Calling code when Node is exiting

process.on('exit', function () {
  setTimeout(function () {
   console.log('This will not run');
  }, 100);
  console.log('Bye.');
});

Because the loop isn’t going to run again, the setTimeout() code will never be evaluated.

An extremely useful event provided by process is uncaughtException (Example 5-15). After you’ve spent any time with Node, you’ll find that exceptions that hit the main event loop will kill your Node process. In many use cases, especially ...