my-only-either

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.

name	category	description
ILeft	type	Left interface
IRight	type	Right interface
Either	type	Either type using ILeft and IRight
TPickLeft	utility type	Return Type of left in Either
TPickILeft	utility type	Return Type of ILeft in Either
TPickRight	utility type	Return Type of right in Either
TPickIRight	utility type	Return Type of IRight in Either
left	function	value convert ILeft type
right	function	value convert IRight type
isLeft	function	check given value is ILeft type
isRight	function	check given value is IRight type

PassFailEither

Name using pass and fail.

name	category	description
IFail	type	Fail interface
IPass	type	Pass interface
PassFailEither	type	PassFailEither type using IFail and IPass
TPickFail	utility type	Return Type of fail in Either
TPickIFail	utility type	Return Type of IFail in Either
TPickPass	utility type	Return Type of pass in Either
TPickIPass	utility type	Return Type of IPass in Either
fail	function	value convert IFail type
pass	function	value convert IPass type
efail	function	value convert IFail type, exactly same fail. If you use jest or test runner this function is helpful for auto import & auto complete
epass	function	value convert IPass type, exactly same pass. If you use jest or test runner this function is helpful for auto import & auto complete
isFail	function	check given value is IFail type
isPass	function	check given value is IPass type

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>;