my-only-either v1.3.0

my-only-either

Simple Type and Function set for Either interface. Either important concept in functional programming. But Node.js and TypeScript don't have implmentation. So you can choose another functional implementation like fp-ts or anther functional utility. But if you need only Eihter, this package is good alternative.

Why? use Either?

Zero Dependency

my-only-either not use package. only 1k(1,489byte) size.

Help functional programming

Helpful for functional programming and integrate return type. See below.

import { parse as jsoncParse } from 'jsonc-parser';
import { parse as json5Parse } from 'json5';

function json5Parse(value: string): PassFailEither<Error, Record<any, any>> {
  try {
    return pass(json5Parse(value));
  } catch (err) {
    return fail(new Error(err));
  }
}

function jsoncParse(value: string): PassFailEither<Error, Record<any, any>> {
  try {
    return pass(jsoncParse(value));
  } catch (err) {
    return fail(new Error(err));
  }
}

function parse(value: string): Record<any, any> {
  const jsoncParsedEither = jsoncParse(value);

  if (isPass(jsoncParsedEither)) {
    return jsoncParsedEither.pass;
  }

  const json5ParsedEither = json5Parse(value);

  if (isPass(json5ParsedEither)) {
    return json5ParsedEither.pass;    
  }

  throw new Error(json5ParsedEither.fail);
}

throw keyword move control-flow. But Either, PassFailEither don't move control-flow besides Either helpful functional programming and function pipe.

Either

Name using left and right.

PassFailEither

Name using pass and fail.

Type order in Eiter, PassFailEither

First type arguments is ILeft or IFail. Because fp-ts and many functional programming language choose first type is left(or fail).

type Either<TLEFT, TRIGHT> = ILeft<TLEFT> | IRight<TRIGHT>;