Add Re-Export An Imported Type as a TypeScript til

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://tinyletter.com/jbranchaud).
 
-_1042 TILs and counting..._
+_1043 TILs and counting..._
 
 ---
 
@@ -50,6 +50,7 @@ _1042 TILs and counting..._
 * [Shell](#shell)
 * [Tailwind CSS](#tailwind-css)
 * [tmux](#tmux)
+* [TypeScript](#typescript)
 * [Unix](#unix)
 * [Vercel](#vercel)
 * [Vim](#vim)
@@ -944,6 +945,10 @@ _1042 TILs and counting..._
 - [tmux in your tmux](tmux/tmux-in-your-tmux.md)
 - [Toggle Between Two Common Sessions](tmux/toggle-between-two-common-sessions.md)
 
+### TypeScript
+
+- [Re-Export An Imported Type](typescript/re-export-an-imported-type.md)
+
 ### Unix
 
 - [All The Environment Variables](unix/all-the-environment-variables.md)

typescript/re-export-an-imported-type.md

@@ -0,0 +1,31 @@
+# Re-Export An Imported Type
+
+I have a TypeScript module that is defining an XState machine. Among other
+things, it imports the `DoneEventObject` type from `xstate`. I want to
+re-export that type so that any modules using this machine have access to that
+type definition.
+
+This can be done a couple of ways. One way to import it under an aliased name
+and then assign + export it using the original name.
+
+```typescript
+import {Machine, DoneEventObject as _DoneEventObject} from 'xstate'
+
+export type DoneEventObject = _DoneEventObject
+```
+
+This works, but adds some potential indirection and confusion through the
+double assignment.
+
+Another way of doing this is to reference the type off the import statement as
+part of an assignment.
+
+```typescript
+import {Machine} from 'xstate'
+
+export type DoneEventObject = import('xstate').DoneEventObject
+```
+
+This imports, assigns, and exports the type in a single statement.
+
+[source](https://github.com/microsoft/TypeScript/issues/28481#issuecomment-552938424)