Episode 7 📺

A facade for side-effects: write test-friendly, async/await-style, JS code.

Care about unit testing around side-effects? You may fall in love with Episode 7.

Episode 7 is a simpler way

• spy on, intercept, & fake async function calls
• avoid brittle HTTP mocks
• confidently handle async errors

A tiny library 🐿

• no production npm dependencies
• <100-lines-of-code (without comments)

Functional in nature 🌲

Inspired by the test-friendly generator architecture of redux-saga and the pure side-effects of Elm.

Requires

ES6/Generator support.

• Known to work in Node.js 6.2
• Should work in any ES6-compliant JavaScript environment

Install

npm install episode-7 --save

Changes

See: CHANGELOG

Usage

const Episode7 = require('episode-7');
const fetch = require('node-fetch');
 
// Compose an Episode 7 Generator for an async call sequence.
//
function* findFirstMovie(searchTerm) {
 
  // Wrap side-effects with Episode 7's `call`
  //
  let results = yield Episode7.call(
    fetchJson,
    `http://www.omdbapi.com/?s=${encodeURIComponent(searchTerm)}`
  );
 
  // Do something programmatic with the result.
  //
  let firstResultId = results.Search[0].imdbID;
  
  // Use that transformed value to make the next call.
  //
  let movie = yield Episode7.call(
    fetchJson,
    `http://www.omdbapi.com/?i=${encodeURIComponent(firstResultId)}`
  );
 
  return movie;
}
 
// Side-effect function,
// a barebones helper to fetch & decode JSON.
//
function fetchJson(url) {
  return fetch(url).then( response => response.json() );
}
 
// Run the generator with Episode 7, returning a promise.
//
Episode7.run(findFirstMovie, 'Episode 7')
  .then( movie => console.log(movie.Title) )
  .catch( error => console.error(error) )

Smooth running tips 🚝

Handle errors

catch after Episode7.run to handle errors from the async flow (log|exit|retry).

Avoid catching within side-effect functions. Allow their errors to bubble up.

Name generator functions

Declare generator functions as named function expressions; this makes stacktraces & error messages more meaningful.

Background

I created this module to make it easy to code & test sequences of web service API requests interleaved with programmatic logic. I'm pulling the essence of redux-saga into the smallest, plainest surface area conceivable.