Describe fork, spawn and exec.
There are three primary ways to create a child process in Node.js:
child_process.exec(): exec spawns a shell and runs a command, then buffers the entire output before passing it to a callback function.
child_process.spawn(): spawn launches a new process and returns a ChildProcess object that provides a streaming interface for communication.
child_process.fork(): This method is a special case of spawn() method to create child processes. It creates a new instance of the V8 engine and the Node.js runtime to execute a specific JavaScript module.