Summary - Error handling

Combine Error, try/catch and custom error to write an error class hierarchy.

Summary - Error handling

In this group you learned the core tools of error handling: the Error class, catching with try/catch, custom error classes, Express error middleware and the unhandledRejection event.

You can combine these five tools to build a solid error handling system. For example, you can define a custom error class and catch it with try/catch. This is the basic pattern for handling errors in a controlled way in Node.js apps. Now you will combine all pieces in one piece of code.

Exercise Write an AppError class and catch it

Define an AppError class that extends Error. In constructor(message) set super(message) and this.name = "AppError". In try throw new AppError("test"), in catch (e) print console.log(e.name).

Show example solution

class AppError extends Error {
  constructor(message) {
    super(message);
    this.name = "AppError";
  }
}
try {
  throw new AppError("test");
} catch (e) {
  console.log(e.name);
}

Test yourself

Match each tool to its role

Error

Base error class
try/catch

Catches errors
extends

Derives a class
error middleware

Express error handler
Which variable holds the error caught by try/catch?
```
catch (e)
```
- The e in catch(e)
- The name in throw
- A global error
- process.err
Show answer

The e in catch(e) — The e in catch(e) holds the thrown error.

Complete the super call

constructor(message) { ____(message); this.name = "AppError"; }

Show answer

constructor(message) { super(message); this.name = "AppError"; }

Next lesson: node:test

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