Rules of the Promised Land

Avoiding Promise Foot-guns

• Function Rules To Live By

  • ALWAYS return - in every sync AND async function.
  • ALWAYS use single argument functions.
  • ALWAYS limit one async call per function - except when using Promise.all() or chaining via .then()
  • return immediately if possible - makes single-purpose more clear.
  • Prefer named parameters w/ destructuring: ({name, phone = 'none'}) => name + ' ' + phone
  • Avoid this - pass needed data as arguments explicitly. Prevents code which is harder to reason about, and bugs related to calling class methods out of order.

• Error Rules To Live By

  • ALWAYS use Error constructor with new keyword - throw new Error('oh no') - capture call stacks.
  • 2 critical rules for .catch()
    • ALWAYS use .catch() - typically once - and usually at the top-most part of your app.
    • Omit in library code - leaving the error handling to the calling application (or test) code.

This list covers 95% of the flaws/bugs I find in Promise code.

Using these rules, with Promises as the glue to stick code together, lets you treat async & sync functions the same. Ultimately your function names help make your code read like a story.

In fancier terms: De-coupled composition at it's finest. :)