result-tuple

result-tuple is a small set of types for Typescript that make it easier to handle success and error return conditions from your functions in a type-safe manner. This is partly inspired by the pattern matching possible in a range of functional languages (for example, Pattern Matching in F#).

Installation

yarn add -D @developertown/result-tuple

Usage

Using ResultTuple, you can define a contract with code calling your function that helps ensure better handling of both success and failure conditions. It also helps avoid mistakes in situations where a function returns a number or string, and truthy/falsey checks have surprising outcomes.

import { ResultTuple, StatusErr, StatusOk, isSuccess, isError } from "@developertown/result-tuple";

const successNoPayload = (): ResultTuple => {
  return [StatusOk];
};

const successWithPayload = (): ResultTuple<string> => {
  return [StatusOk, "Hello world!"];
};

const functionReturningAnError = (): ResultTuple => {
  return [StatusErr, new Error("oh no!")];
};


// ResultStatus type guards:
{
  const result = successNoPayload();
  if (isSuccess(result)) {
    console.log("Success!");
  } else {
    const [, err] = result;
    // note the automatic typing here - if it was not success
    // it must be failure, and the compiler can determine that
    // the destructured second element of the tuple must be an Error object
    console.log("Oh no, the error message was", err.message);
  }
}

// "Fire and forget" calling patterns
// When a function returns a value, but the caller doesn't need the value
// but does need to check success
{
  const [status] = successWithPayload();
  if (status === StatusOk) {
    console.log("It worked!");
  }
}

// Handling errors
{
  const result = functionReturningAnError();
  if (isError(result)) {
    const [, err] = result;
    // log it and toss it up to the next level
    console.log("Oh no, we got an error:", err.message);
    throw err;
  }
}

API

ResultTuple<P, E, T>

ResultTuple accepts up to 3 (optional) type arguments:

• P: Payload Type. If your function returns a result value in addition to a result status of StatusOk or StatusErr, define it here. For example, ResultTuple<number> will define a return type (for happy path) of [StatusOk, number].
• E: Error Type. This defaults to the standard Error type, but you can override this with other types if you wish. By default, ResultStatus<number> might return [StatusErr, Error], but you could override with ResultStatus<number, string> to return a simple message instead.
• T: Status Type. While not recommended to override, this defaults to the standard values of StatusOk | StatusErr.

StatusOk

This is defined as both a type alias and a const literal value pointing to the enum value ResultStatus.Ok.

StatusErr

This is defined as both a type alias and a const literal value pointing to the enum value ResultStatus.Err.

isSuccess(result: ResultTuple<any, any, any>)

This is a type guard function that will evaluate whether or not a particular result indicates success. This is useful to let TS automatically type the result value based on the outcome of this call in a conditional.

isError(result: ResultTuple<any, any, any>)

This is a type guard function that will evaluate whether or not a particular result indicates an error. This is useful to let TS automatically type the result value based on the outcome of this call in a conditional.

Contributing

Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

Please make sure to update tests as appropriate.

License

MIT