pipeable-promises

Hello

This module is a couple of simple functions that allow you to handle promises inside Lodash/Ramda pipelines. It's designed to allow function chaining and point-free handling of promises inline with your synchronous code pipes.

This library tries to support built-in promises, rather than replacing them with an alternate async mechanism.

Includes TypeScript definitions.

API

• then(fn)(promise): Attaches fn to the then method of a promise
• catchP(fn)(promise): Attaches fn to the catch method of a promise
• forkP(fn1, fn2)(promise): Runs fn1 if the promise errors, and fn2 if the promise succeeds. Useful for converting a promise to an Either via e.g., Sanctuary.

Examples

Promises

const flow = require('lodash/fp').flow;

flow(
  (n) => Promise.resolve(n),
  then((n) => n / 2),
  then((n) => expect(n).toEqual(21)),
)(42);
// Promise(21)

Catching errors

flow(
  (n) => Promise.reject(n),
  then((n) => n / 2),
  catchP((n) => n),
)(42);
// Promise(21)

Try/catch

The forkP function follows left/right Either semantics, so the rejection branch is the first function, and the resolution branch is the second function.

flow(
  (n: number) => Promise.resolve(n),
  forkP(double, halve),
)(42);
// Promise(21)

flow(
  (n: number) => Promise.reject(n),
  forkP(double, halve),
)(42);
// Promise(84)

Sanctuary Maybe/Either types

The module is designed to integrate with Sanctuary in a point-free style.

flow(
  (n: number): Promise<number> => Promise.resolve(n),
  then((n) => Promise.resolve(n / 2)),
  then(S.Right)
)(42);
// Promise(Right(21))

You can also convert promises to Sanctuary types with forkP, which performs a one-step then/catch on a promise:

flow(
  (n) => Promise.resolve(n),
  then((n) => Promise.resolve(n / 2)),
  forkP(S.Left, S.Right),
)(42);
// Promise(Right(21))