eurgh – strongly-typed errors for TypeScript

A simple convenience package offering strongly-typed customer errors to uses in TypeScript. You can embed a cause which is any Error that you want to encapsulate which is super useful for debugging nested try/catch/throw.

When is this useful?

Using Node or Browser built-in Error types is just cumbersome and weak in terms of flexibility. Eurgh is a lightweight library that contains a generic base class TypedError<Name, Code, Data> which is extended by multiple errors such as NotFoundError, ValidationError, UnauthorizedError, etc.

Extending with your own custom errors

Obviously, you can extend TypedError and create your own custom typed error(s). For example, to create a TimeoutError:

import { TypedError } from "eurgh"

export class TimeoutError extends TypedError<
	"TIMEOUT",
	408,
	{ timeout: number; operation?: string }
> {
	constructor(timeout: number, operation?: string, cause?: Error) {
		const message = [
			`Timeout of ${timeout.toLocaleString()}ms exceeded`,
			operation ? `for operation "${operation}"` : ``,
		]
			.join(` `)
			.trim()

		super(`TIMEOUT`, 408, { timeout, operation }, message, cause)
	}
}

// And you can then throw it from anywhere in your project
try {
	throw new TimeoutError(1000)
	throw new TimeoutError(1000, `callRestApi`)
} catch (error) {
	if (error instanceof TimeoutError) {
		// handle it
	}
}

Shape

All of our errors implement the below interface, often narrowing it down further for strong error typing:

// The basic shape of any error from Eurgh
export interface Shape {
	message: string
	kind: string
	code: number
	data: any
	stack?: string
	cause?: Cause
}

// The generic interface implemented by our TypedError base class.
export interface GenericErrorShape<K extends string, C extends number, D extends any>
	extends ErrorShape {
	kind: K
	code: C
	data: D
}

// All custom errors extend TypedError which is defined as follows
export class TypedError<
	K extends string = string, 	// the string literal for the error's kind
	C extends number = number, 	// the number literal for the error's code
	D extends any = any 		// the data field containing the metadata for further debugging
> extends Error implements GenericErrorShape<K, C, D>

Error Messages

Personally, I simply prefer to hide each custom error's message from the caller. That way, I normalize the way each error kind outputs its message. And you provide the input by typing your custom error's constructor.

You can always add more flexibility by allowing a message: string argument, or a more lax static factory method.

Why the name eurgh?

Mostly because:

1. it kinda sounds like err
2. it is a sound I make when I see random unexpected errors, ha

Finally, this is a package mostly built to be used in my own microservices. (I got tired of recreating and copy-pasting the same files from project to project.)