There is this import found at line#2 in Changesets CLI package source code

import { ExitError, InternalError } from "@changesets/errors";

You will learn the below concepts:

1. ExtendableError package
2. ExitError
3. InternalError

ExtendableError

You will find that ExitError extends ExtendableError.

I assumed ExtendableError is probably another class defined within the same file, that was not the case.

It is imported from extendable-error. What’s this?

A simple abstract extendable error class that extends Error, which handles the error name, message and stack property.

Install

npm install extendable-error - save

Usage

This usage example from the docs.

import ExtendableError from 'extendable-error';

class SomeError extends ExtendableError {
 constructor(
 message: string,
 public code: number
 ) {
 super(message);
 }
}

let someError = new SomeError('Some error', 0x0001);

Purpose of ExtendableError is to create custom error classes in JavaScript
with consistent behavior for error handling. ExtendableError preserves the error stack and name.

Extending ExtendableError vs Extending Error

I asked ChatGPT to list the differences between extending ExtendableError and extending Error directly and below is picked from the ChatGPT answer:

name Property Mismatch (In Some Environments):

Direct Error Inheritance: In some older JavaScript environments (e.g., older versions of Node.js or some non-browser environments), if you extend Error directly, the name property might not always be correctly set to the name of the error class (e.g., ValidationError).
ExtendableError: It explicitly sets this.name = this.constructor.name;, which ensures that the name property is set correctly across all environments, even if the environment doesn’t behave correctly
with Error inheritance.

2. Stack Trace Reliability:

Direct Error Inheritance: In some environments, especially Node.js, using Error.captureStackTrace directly in your custom error class ensures the stack trace points to the custom error class. If you
don’t use this, the stack trace might not behave as expected and could potentially show the wrong location in the call stack.
ExtendableError: By using Error.captureStackTrace, ExtendableError ensures that the stack trace is correctly generated, pointing to the location where the error was thrown. This is critical in environments
like Node.js where debugging is more reliant on stack traces.

ExitError

The below code is picked from Changesets errors package

export class ExitError extends ExtendableError {
 code: number;
 constructor(code: number) {
 super(`The process exited with code: ${code}`);
 this.code = code;
 }
}

InternalError

The below code is picked from Changets errors package

export class InternalError extends ExtendableError {
 constructor(message: string) {
 super(message);
 }
}

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ExtendableError usage in changesets errors package