maybe-combine-errors

Combine 0 or more errors into one.

Usage

const combine = require('maybe-combine-errors')

const err1 = new Error('one')
const err2 = new Error('two')

console.log(combine([err1, err2]).message)
console.log(combine([err1, err2]) instanceof Error)
console.log(combine([err1, null]) === err1)
console.log(combine([]) === undefined)

throw combine([err1, err2])

$ node example.js
one; two
true
true
true
example.js:9
throw combine([err1, err2])
^

Error: one
    at Object.<anonymous> (example.js:3:14)
    at Module._compile (internal/modules/cjs/loader.js:945:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:962:10)
    at Module.load (internal/modules/cjs/loader.js:798:32)
    at Function.Module._load (internal/modules/cjs/loader.js:711:12)
    at Function.Module.runMain (internal/modules/cjs/loader.js:1014:10)
    at internal/main/run_main_module.js:17:11

Error: two
    at Object.<anonymous> (example.js:4:14)
    at Module._compile (internal/modules/cjs/loader.js:945:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:962:10)
    at Module.load (internal/modules/cjs/loader.js:798:32)
    at Function.Module._load (internal/modules/cjs/loader.js:711:12)
    at Function.Module.runMain (internal/modules/cjs/loader.js:1014:10)
    at internal/main/run_main_module.js:17:11

API

`combine(errors)`

The errors argument must be an array.

Elements that are null or undefined are skipped. If the array is empty (after skipping null and undefined), undefined will be returned. If the array contains only 1 error, that error will be returned as-is. Otherwise, a combined error with joined messages and a lazily joined stack. Duplicate messages are skipped.

Respects transient-error and err.expected: if all errors have .transient === true then the combined error will also be transient. Same for .expected, which is useful for the following pattern:

if (err.expected) {
  console.error(err.message)
  process.exit(1)
} else {
  throw err
}

Alternatives

`combine-errors`

Same message and stack behavior. Different in that it always returns an error regardless of input length.

`aggregate-error`

Sets message to a joined stack, which means you can't get a human-friendly message with e.g. console.error(err.message). Removes "mostly unhelpful" internal Node.js entries from the stack.

Install

With npm do:

npm install maybe-combine-errors