This lesson's interactive features are locked, please to keep using them

Help and Exit

A REPL is only useful if it does something! Our REPL will work using the concept of "commands". A command is a single word that maps to an action.

We're going to support two commands in this step:

help: prints a help message describing how to use the REPL
exit: exits the program

Assignment

Remove your logic that prints the first word (the command) back to the user
Add a callback for the exit command. Commands in our REPL are just callback functions. I created a command_exit.ts file and added a function:

export function commandExit();

This function should print Closing the Pokedex... Goodbye! then immediately exit the program. I used process.exit(0) to exit the program.

Create a "registry" of commands. This will give us a nice abstraction for managing the many commands we'll be adding. I created a type that describes a command:

export type CLICommand = {
  name: string;
  description: string;
  callback: (commands: Record<string, CLICommand>) => void;
};

Then I created an object literal of supported commands:

export function getCommands(): Record<string, CLICommand> {
  return {
    exit: {
      name: "exit",
      description: "Exit the Pokedex",
      callback: commandExit,
    },
    // can add more commands here
  };
}

Register the exit command. Update your REPL loop to use the "command" the user typed in to look up the callback function in the registry. If the command is found, call the callback (and log any errors that are thrown). If there isn't a handler, just print Unknown command.
Test your program (obviously).
Add a help command, its callback, and register it. It should print:

Welcome to the Pokedex!
Usage:

help: Displays a help message
exit: Exit the Pokedex

Generate the "usage" section by iterating over my registry of commands. That way the help command will always be up-to-date with the available commands. I recommend:

Put your handler callback functions in their own files (e.g. command_exit.ts, command_help.ts)
Pass the command registry to the callback functions (although exit will ignore it) like this export function commandHelp(commands: Record<string, CLICommand>)
Define the CLICommand type in its own file (e.g. command.ts)
You can import types explicitly in TypeScript like this: import type { CLICommand } from "./command.js";

Test your code again manually.

Run and submit the CLI tests from the root of the repo.