chore: comments regarding Readonly usage

2019-11-02 10:40:08 -04:00
parent 26c859aedd
commit abdaf10d88
2 changed files with 5 additions and 0 deletions
--- a/packages/runtime-core/src/apiWatch.ts
+++ b/packages/runtime-core/src/apiWatch.ts
@@ -68,6 +68,9 @@ export function watch<T>(
 ): StopHandle

 // overload #3: array of multiple sources + cb
+// Readonly constraint helps the callback to correctly infer value types based
+// on position in the source array. Otherwise the values will get a union type
+// of all possible value types.
 export function watch<T extends Readonly<WatcherSource<unknown>[]>>(
  sources: T,
  cb: WatchHandler<MapSources<T>>,