Mastering Error Handling: How to Show Custom Errors for a Node.js CLI App Made Using Commander

Commander is an amazing tool for building Node.js CLI apps. With its simple and intuitive API, you can create powerful command-line interfaces that make your users’ lives easier. But, have you ever wondered how to handle errors in a way that’s both informative and user-friendly? In this article, we’ll dive into the world of custom error handling for Node.js CLI apps made using Commander.

Why Custom Error Handling Matters

When building a CLI app, it’s essential to consider the user experience. A good error message can make all the difference between a frustrated user and a happy one. Custom error handling allows you to provide more context, suggest solutions, and even add a touch of personality to your app’s output.

The Default Error Handling: Not Good Enough?

By default, Commander will display a rather bland error message when something goes wrong. For example, if a user provides an invalid option, they’ll see something like this:

error: unknown option `-- invalid.option`

This error message doesn’t provide much context, and it certainly doesn’t make the user feel welcome. We can do better!

Creating Custom Errors with Commander

Commander provides a few ways to customize error handling. Let’s explore them together.

1. The `error` Event

The `error` event is emitted by Commander when an error occurs. You can listen to this event and handle errors accordingly. Here’s an example:

const program = require('commander');

program
  .command('my-command')
  .option('--my-option ')
  .action((options) => {
    // Your command logic goes here
  });

program.on('error', (err) => {
  console.error(`Oops! An error occurred: ${err.message}`);
  process.exit(1);
});

In this example, we’re listening to the `error` event and logging a custom error message to the console. We’re also exiting the process with a non-zero status code, indicating that an error occurred.

2. Custom Error Messages with `program.outputHelp()`

Another way to customize error handling is by using the `program.outputHelp()` method. This method allows you to display a custom error message and the command’s help text. Here’s an example:

const program = require('commander');

program
  .command('my-command')
  .option('--my-option ')
  .action((options) => {
    // Your command logic goes here
  });

program.on('error', (err) => {
  console.error(`Error: ${err.message}`);
  program.outputHelp();
  process.exit(1);
});

In this example, we’re displaying a custom error message and then calling `program.outputHelp()` to show the command’s help text. This can be useful for providing more context to the user.

3. Custom Error Handling with `command.on(‘error’)`

You can also handle errors on a per-command basis using the `command.on(‘error’)` event. This allows you to provide custom error handling for specific commands. Here’s an example:

const program = require('commander');

const myCommand = program
  .command('my-command')
  .option('--my-option ')
  .action((options) => {
    // Your command logic goes here
  });

myCommand.on('error', (err) => {
  console.error(`Error in my-command: ${err.message}`);
  process.exit(1);
});

In this example, we’re handling errors specifically for the `my-command` command. This allows us to provide custom error handling for each command in our CLI app.

Best Practices for Custom Error Handling

Now that we’ve explored the different ways to customize error handling in Commander, let’s discuss some best practices to keep in mind:

• Be clear and concise**: Error messages should be easy to understand and concise. Avoid using technical jargon or overly complex language.
• Provide context**: Try to provide more context about the error, such as the specific option or command that caused the issue.
• Be friendly and approachable**: Error messages should be friendly and approachable. Avoid using language that might come across as abrasive or confrontational.
• Test your error handling**: Make sure to test your custom error handling to ensure it works as expected.

program.on('error', (err) => {
  console.error(`Error: ${err.message} (Code: ${err.code})`);
  process.exit(err.code);
});

class CustomError extends Error {
  constructor(message, code) {
    super(message);
    this.code = code;
  }
}

program.on('error', (err) => {
  if (err instanceof CustomError) {
    console.error(`Error: ${err.message} (Code: ${err.code})`);
    process.exit(err.code);
  } else {
    console.error(`Unknown error: ${err.message}`);
    process.exit(1);
  }
});