fix: type of base argument create error (#108)

* Fix type of Base argument to createError

* Update README for fix to type of Base arg

* Use ErrorConstructor for type of Base

* Update README

README.md

@@ -22,7 +22,7 @@ createError(code, message [, statusCode [, Base]])
 - `code` (`string`, required) - The error code, you can access it later with `error.code`. For consistency, we recommend prefixing plugin error codes with `FST_`
 - `message` (`string`, required) - The error message. You can also use interpolated strings for formatting the message.
 - `statusCode` (`number`, optional) - The status code that Fastify will use if the error is sent via HTTP.
-- `Base` (`Error`, optional) - The base error object that will be used. (eg `TypeError`, `RangeError`)
+- `Base` (`ErrorConstructor`, optional) - The base error object that will be used. (eg `TypeError`, `RangeError`)
 
 ```js
 const createError = require('@fastify/error')

types/index.d.ts

@@ -2,21 +2,21 @@ declare function createError<C extends string, SC extends number, Arg extends un
   code: C,
   message: string,
   statusCode: SC,
-  Base?: Error
+  Base?: ErrorConstructor
 ): createError.FastifyErrorConstructor<{ code: C, statusCode: SC }, Arg>
 
 declare function createError<C extends string, Arg extends unknown[] = [any?, any?, any?]> (
   code: C,
   message: string,
   statusCode?: number,
-  Base?: Error
+  Base?: ErrorConstructor
 ): createError.FastifyErrorConstructor<{ code: C }, Arg>
 
 declare function createError<Arg extends unknown[] = [any?, any?, any?]> (
   code: string,
   message: string,
   statusCode?: number,
-  Base?: Error
+  Base?: ErrorConstructor
 ): createError.FastifyErrorConstructor<{ code: string }, Arg>
 
 type CreateError = typeof createError

types/index.test-d.ts

@@ -65,3 +65,7 @@ expectError(new CustomTypedArgError6('a', 'b'))
 expectError(new CustomTypedArgError6('a', 'b', 'c'))
 CustomTypedArgError6('a', 'b', 'c', 'd')
 expectError(new CustomTypedArgError6('a', 'b', 'c', 'd', 'e'))
+
+
+const CustomErrorWithErrorConstructor = createError('ERROR_CODE', 'message', 500, TypeError)
+expectType<FastifyErrorConstructor<{ code: 'ERROR_CODE', statusCode: 500 }>>(CustomErrorWithErrorConstructor)