Add useReused hook as a monadic way of accessing CustomHook.reusableDeps

library/coreGeneric/src/main/scala/japgolly/scalajs/react/hooks/extra.scala

@@ -54,18 +54,27 @@ trait extra {
     HookResult(UseRef.unsafeCreateToJsComponent(a))    
 
   /**
-  * Returns a stateful value, and a function to update it.
-  *
-  * During the initial render, the returned state is the same as the value passed as the first
-  * argument (initialState).
-  *
-  * During subsequent re-renders, the first value returned by useState will always be the most recent
-  * state after applying updates.
-  */
+    * Returns a stateful value, and a function to update it.
+    *
+    * During the initial render, the returned state is the same as the value passed as the first
+    * argument (initialState).
+    *
+    * During subsequent re-renders, the first value returned by useState will always be the most recent
+    * state after applying updates.
+    */
   @inline final def useStateWithReuse[S: ClassTag: Reusability](
     initialState: => S
   ): HookResult[UseStateWithReuse[S]] =
     HookResult(UseStateWithReuse.unsafeCreate(initialState))
 
+  /**
+    * Given a reusable value, returns the original value that is being reused whenver reusability
+    * applies, together with a revisition a number that increments only when the value isn't reused.
+    *
+    * Useful for using `Reusability` logic in facades to JS hooks that accept dependencies: you can
+    * pass the revision as a dependency to the JS hook.
+    */
+  @inline final def useReused[D: Reusability](deps: => D): HookResult[(D, Int)] =
+    CustomHook.reusableDeps[D].toHookResult(() => deps)
 
 }

library/tests/src/test/scala/japgolly/scalajs/react/core/HooksTest.scala

@@ -2054,7 +2054,29 @@ object HooksTest extends TestSuite {
     }
   }
 
-  def testFromFunction() = {
+  private def testUseReused(): Unit = {
+    implicit val reusePIByRounding: Reusability[PI] = Reusability.by(_.pi / 2) 
+
+    val comp = ScalaFnComponent[Unit] { _ =>
+      for {
+        count <- useState(PI(0))
+        reused <- useReused(count.value)
+        (stable, rev) = reused
+      } yield
+        <.div(
+          <.div(s"count=${count.value}, stable=$stable, rev=$rev"),
+          <.button(^.onClick --> count.modState(_ + 1))
+        )
+    }
+
+    test(comp()) { (t) =>
+      t.assertText("count=PI(0), stable=PI(0), rev=1")
+      t.clickButton(1); t.assertText("count=PI(1), stable=PI(0), rev=1")
+      t.clickButton(1); t.assertText("count=PI(2), stable=PI(2), rev=2")
+    }
+  }  
+
+  private def testFromFunction() = {
     val jsHook1: js.Function1[Int, Int] = _ + 1
     val jsHook2: js.Function2[Int, Int, String] = (a: Int, b: Int) => (a + b).toString
 
@@ -2210,6 +2232,7 @@ object HooksTest extends TestSuite {
     "renderWithReuse (monadic alternative using Render.memo)" - {
       "main" - testMonadicRenderWithReuse()
     }
+    "useReused" - testUseReused()
     "fromFunction" - testFromFunction()
   }
 }

project/build.properties

@@ -0,0 +1 @@
+sbt.version=1.10.6