TsErrorFlow

A one file, zero-dependency library for improved control flow and error handling in TypeScript. In fact, the entire code base is only 43 lines including comments. Inspired by the concepts of Railway Oriented Programming.

TsErrorFlow leverages Union Types, Intersection Types, and User-Defined Type Guards to provide an intuitive and type safe developer experience for error handling.

Usage

TsErrorFlow allows you to represent the potential errors in your application domain using plain old javascript objects. This makes it easier to follow a more explicit coding style in which relevant information about things that went wrong can be passed simply and acted on, instead of relying on throwing Errors for control flow:

interface ParkingLotFullError = {
    tryAgainAt: Date;
}

interface Ticket {
    ticketNumber: string;
    issuedAt: Date;
}

function tryGetTicket(): Ticket | ParkingLotFullError {
    if (lotIsFull()) {
        return makeError({
            tryAgainAt: new Date()
        });
    } 

    // return an actual ticket
}

const ticketResponse = tryGetTicket();

if (isError<Ticket, ParkingLotFullError>(ticketResponse)) {
    // response is definitely an error and will only allow access of properties from ParkingLotFullError
} else {
    // response is definitely a ticket and will only allow access of properties from Ticket
}