Added support for cause (#116)

* Added support for cause

* Removed console.error

* Added support for cause w/o changing signature

* Removed hasCause from types

* Removed an extra hasCause

* Removed extra comma

* Documentation change

* Fix for node v14

* Applied lint fix

---------

Co-authored-by: Daniele Fedeli <danielefedeli@MacBook-Air.station>

Author: DanieleFedeli

README.md

@@ -37,6 +37,15 @@ const CustomError = createError('ERROR_CODE', 'Hello %s')
 console.log(new CustomError('world')) // error.message => 'Hello world'
 ```
 
+How to add cause:
+```js
+const createError = require('@fastify/error')
+const CustomError = createError('ERROR_CODE', 'Hello %s')
+console.log(new CustomError('world', {cause: new Error('cause')})) 
+// error.message => 'Hello world'
+// error.cause => Error('cause')
+```
+
 ### TypeScript
 
 It is possible to limit your error constructor with a generic type using TypeScript:

benchmarks/instantiate.js

@@ -7,10 +7,12 @@ const FastifyError = createError('CODE', 'Not available')
 const FastifyError1 = createError('CODE', 'Not %s available')
 const FastifyError2 = createError('CODE', 'Not %s available %s')
 
+const cause = new Error('cause')
 new benchmark.Suite()
   .add('instantiate Error', function () { new Error() }, { minSamples: 100 }) // eslint-disable-line no-new
   .add('instantiate FastifyError', function () { new FastifyError() }, { minSamples: 100 }) // eslint-disable-line no-new
   .add('instantiate FastifyError arg 1', function () { new FastifyError1('q') }, { minSamples: 100 }) // eslint-disable-line no-new
   .add('instantiate FastifyError arg 2', function () { new FastifyError2('qq', 'ss') }, { minSamples: 100 }) // eslint-disable-line no-new
+  .add('instantiate FastifyError cause', function () { new FastifyError2({ cause }) }, { minSamples: 100 }) // eslint-disable-line no-new
   .on('cycle', function onCycle (event) { console.log(String(event.target)) })
   .run({ async: false })

index.js

@@ -17,10 +17,16 @@ function createError (code, message, statusCode = 500, Base = Error) {
     if (!new.target) {
       return new FastifyError(...args)
     }
+
     this.code = code
     this.name = 'FastifyError'
     this.statusCode = statusCode
 
+    const lastElement = args.length - 1
+    if (lastElement !== 1 && args[lastElement] && typeof args[lastElement] === 'object' && 'cause' in args[lastElement]) {
+      this.cause = args.pop().cause
+    }
+
     this.message = format(message, ...args)
 
     Error.stackTraceLimit !== 0 && Error.captureStackTrace(this, FastifyError)

test/index.test.js

@@ -152,3 +152,23 @@ test('Create the error without the new keyword', t => {
   t.equal(err.statusCode, 500)
   t.ok(err.stack)
 })
+
+test('Create an error with cause', t => {
+  t.plan(2)
+  const cause = new Error('HEY')
+  const NewError = createError('CODE', 'Not available')
+  const err = NewError({ cause })
+
+  t.ok(err instanceof Error)
+  t.equal(err.cause, cause)
+})
+
+test('Create an error with last argument null', t => {
+  t.plan(2)
+  const cause = new Error('HEY')
+  const NewError = createError('CODE', 'Not available')
+  const err = NewError({ cause }, null)
+
+  t.ok(err instanceof Error)
+  t.notOk(err.cause)
+})

types/index.test-d.ts

@@ -69,3 +69,4 @@ expectError(new CustomTypedArgError6('a', 'b', 'c', 'd', 'e'))
 
 const CustomErrorWithErrorConstructor = createError('ERROR_CODE', 'message', 500, TypeError)
 expectType<FastifyErrorConstructor<{ code: 'ERROR_CODE', statusCode: 500 }>>(CustomErrorWithErrorConstructor)
+CustomErrorWithErrorConstructor({cause: new Error('Error')})