Learn TypeScript 3 by Building Web Applications

Implementing the UnreachableCaseError class

We'll create a common package for this class. This will represent a layer of code that is shared between different parts of our code base:

1. Create an src/common folder.
2. Create an errors folder under src/common.

Inside the src/common/errors folder, do the following: Create a file called unreachable-case-error.ts. Here's the code:

export class UnreachableCaseError extends Error { 
    constructor(val: never) { 
        super(`Unreachable case: ${val}`); 
    } 
} 

Next, do the following:

1. Create a barrel for the errors package and export the UnreachableCaseError class.
2. Create a barrel for the common package and re-export everything from the errors package using export * from ./errors.

With this done, we'll be ...