Reimplementation of Elm's RemoteData http://package.elm-lang.org/packages/krisajenkins/remotedata/latest

remoteData.js

// @flow
// https://flowtype.org/try/#0PTAEAEDMBsHsHcBQiCmAPADrATgF1LgJ4YqgBKKAtrLigCICGuDAPAKLbY4AqxKANKABqDaAFcUvEgD5QAXkShQAH1ABvUAGdmtAFygA5ADsaAQU0BrFABMDoAL6KV6rTpT6DcBtYCWRgOZ2jkqqGtpM7oaQDD7i2CgGgiicOPocXNhSpMHOYW4emmIAxkUompqJoABuohL6IuKSfA4A3MjoWHigkGJGRbg+sEagJrjmVtbsKZl8gg0SWdIAFACU+hTUtIzMUxlZc7VNMupO8bhi2MN5ER6j4zZBbY6omDj4PX0DQ6BevgG7PFmwkOi1W6yoNHoTFY6UBJAOjUWJyUZwuV1cN0Mvz8gVaiGeHTe3V6-UGw2isQuKABM3hwMRfGWyQyaWmWTW5AhW2hNP29IWjORoFRlxc4T0URicQSSWmeIJry6H1J30KJTKml5QPmRxQyxqjXqIL4HI2kO2MLZ2uNxzUpxQ51F1wlBjVpXKlQNEnlyGgDu6sFg4M2UJ22mwOME4ZxsjkWmK7s0SwMDHg8FAhBQDAAFgYVm1IIH5N0pVTk7BsyNA3mC0W49iAqta7Bi3dLDYm0A

export type RemoteData<ErrorType, ValueType> =
  | { state: 'notAsked' }
  | { state: 'loading' }
  | { state: 'failure', error: ErrorType }
  | { state: 'success', value: ValueType };

export function notAsked<ErrorType, ValueType>(): RemoteData<ErrorType, ValueType> {
  return { state: 'notAsked' };
}

export function loading<ErrorType, ValueType>(): RemoteData<ErrorType, ValueType> {
  return { state: 'loading' };
}

export function failure<ErrorType, ValueType>(error: ErrorType): RemoteData<ErrorType, ValueType> {
  return { state: 'failure', error };
}

export function success<ErrorType, ValueType>(value: ValueType): RemoteData<ErrorType, ValueType> {
  return { state: 'success', value };
}

let foo: RemoteData<string, string> = success('aww yeah');
foo = failure('oh noo');
foo = loading();
foo = notAsked();