Added optional formatting function param

facebook · Jan 17, 2019 · 2ea796e · 2ea796e
1 parent 8041867
commit 2ea796e
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Showing 2 changed files with 25 additions and 4 deletions.
diff --git a/lib/react.js b/lib/react.js
@@ -321,7 +321,10 @@ declare module react {
 
   declare export function useRef<T>(initialValue: ?T): {current: T | null};
 
-  declare export function useDebugValue(value: any): void;
+  declare export function useDebugValue(
+    value: any,
+    formatterFn: ?(value: any) => any,
+  ): void;
 
   declare export function useEffect(
     create: () => MaybeCleanUpFn,

diff --git a/tests/react/useDebugValue_hook.js b/tests/react/useDebugValue_hook.js
@@ -2,7 +2,25 @@
 
 import React from 'react';
 
-const undefinedValue = React.useDebugValue(123);
+{
+  // Accepts any type of value
+  React.useDebugValue('abc');
+  React.useDebugValue(123);
+  React.useDebugValue(true);
+  React.useDebugValue(['a','b','c']);
+  React.useDebugValue({foo: 1, bar: 2});
+}
 
-(undefinedValue: typeof undefined); // Ok
-(undefinedValue: string); // Error: undefined is incompatible with string
+{
+  // Has an undefined return type
+  ((React.useDebugValue(123)): typeof undefined);
+}
+
+{
+  // Supports optional formatting function
+  const date = new Date();
+  React.useDebugValue(
+    date,
+    date => date.toDateString(),
+  );
+}