Add renderIfTrue and renderIfFalse convenience functions

Both provide a shortcut to render content if a given
boolean flow's value is `true` or `false` respectively.

core/src/jsMain/kotlin/dev/fritz2/core/rendercontext.kt

@@ -58,6 +58,44 @@ interface RenderContext : WithJob, WithScope {
         }
     }
 
+    /**
+     * Renders the data of a boolean [Flow] only if it's value is `true`.
+     *
+     * @receiver [Flow] containing the data
+     * @param into target to mount content to. If not set a child div is added to the [Tag] this method is called on
+     * @param content [RenderContext] for rendering the data to the DOM
+     *
+     * @see renderIf
+     * @see renderIfFalse
+     */
+    fun Flow<Boolean>.renderIfTrue(
+        into: Tag<HTMLElement>? = null,
+        content: Tag<*>.() -> Unit
+    ) {
+        renderIf(predicate = { it }, into) { _ ->
+            content()
+        }
+    }
+
+    /**
+     * Renders the data of a boolean [Flow] only if it's value is `false`.
+     *
+     * @receiver [Flow] containing the data
+     * @param into target to mount content to. If not set a child div is added to the [Tag] this method is called on
+     * @param content [RenderContext] for rendering the data to the DOM
+     *
+     * @see renderIf
+     * @see renderIfTrue
+     */
+    fun Flow<Boolean>.renderIfFalse(
+        into: Tag<HTMLElement>? = null,
+        content: Tag<*>.() -> Unit
+    ) {
+        renderIf(predicate = { !it }, into) { _ ->
+            content()
+        }
+    }
+
     /**
      * Renders the non-null data of a [Flow].
      *

core/src/jsTest/kotlin/dev/fritz2/core/rendercontext.kt

@@ -96,6 +96,84 @@ class RenderContextTests {
         assertNull(div(div2))
     }
 
+    @Test
+    fun testRenderIfTrueFunction() = runTest {
+        val store = storeOf(true)
+
+        val id = Id.next()
+        val expectedContentIfTrue = "rendered"
+        val expectedContentIfFalse = ""
+
+
+        render {
+            div(id = id) {
+                store.data.renderIfTrue(into = this) {
+                    +expectedContentIfTrue
+                }
+            }
+        }
+
+
+        delay(100)
+
+        val divContent = document.getElementById(id)?.textContent
+        assertEquals(
+            expected = expectedContentIfTrue,
+            actual = divContent,
+            message = "Content must be present"
+        )
+
+
+        store.update(false)
+        delay(100)
+
+        val divContentAfterUpdate = document.getElementById(id)?.textContent
+        assertEquals(
+            expected = expectedContentIfFalse,
+            actual = divContentAfterUpdate,
+            message = "Content must be absent"
+        )
+    }
+
+    @Test
+    fun testRenderIfFalseFunction() = runTest {
+        val store = storeOf(false)
+
+        val id = Id.next()
+        val expectedContentIfFalse = "rendered"
+        val expectedContentIfTrue = ""
+
+
+        render {
+            div(id = id) {
+                store.data.renderIfFalse(into = this) {
+                    +expectedContentIfFalse
+                }
+            }
+        }
+
+
+        delay(100)
+
+        val divContent = document.getElementById(id)?.textContent
+        assertEquals(
+            expected = expectedContentIfFalse,
+            actual = divContent,
+            message = "Content must be present"
+        )
+
+
+        store.update(true)
+        delay(100)
+
+        val divContentAfterUpdate = document.getElementById(id)?.textContent
+        assertEquals(
+            expected = expectedContentIfTrue,
+            actual = divContentAfterUpdate,
+            message = "Content must be absent"
+        )
+    }
+
     @Test
     fun testRenderNotNullFunction() = runTest {
         val store = storeOf<String?>(null)