add more tests and comment

Author: Freymaurer

src/Feliz/Html.fs

@@ -12,7 +12,7 @@ module HtmlHelper =
     let inline createElementWithChildren (tag: string) (children: seq<ReactElement>) =
         ReactLegacy.createElement(tag, children = children)
 
-    /// Iterates once, returns (firstMatch, restWithoutMatch).
+    /// This function changes the order of the input array. Last item replaces children key, then we remove the last item.
     let extractByKeyFast (key: string) (arr: seq<(string * obj)>) : (string * obj)[] * (string * obj) option =
         Fable.Core.JsInterop.emitJsStatement (arr, key) """const arrNext_ = Array.from($0);
             for (let i = 0; i < arrNext_.length; i++) {

tests/Feliz/ExtractChildren.test.fs

@@ -101,3 +101,47 @@ describe "HtmlHelper.createElement" <| fun _ ->
         let propsContainChildren: bool = extractedProps |> Array.exists (fun (k, _) -> k = "children")
         expect(propsContainChildren).toBeFalsy()
         expect(extractedProps.Length).toBe((props |> Seq.length) - 1)
+
+    test "extract as last" <| fun _ ->
+        let child = [ Html.span []; Html.div [] ] 
+        let props = 
+            [
+                "id", box "my-div"
+                "data-test", box true
+                "style", box {| color = "red" |}
+                "onClick", box (fun _ -> ())
+                "tabIndex", box 0
+                "className", box "container"
+                "children", box child
+            ]
+        let extractedProps, childOption = HtmlHelper.extractByKeyFast "children" props
+        expect(child).toBeTruthy()
+        let key, child =
+            match childOption with
+            | Some kvp -> kvp
+            | None -> failwith "Expected to find 'children' key"
+        expect(key).toBe("children")
+        expect(child).toEqual(child)
+        let propsContainChildren: bool = extractedProps |> Array.exists (fun (k, _) -> k = "children")
+        expect(propsContainChildren).toBeFalsy()
+        expect(extractedProps.Length).toBe((props |> Seq.length) - 1)
+
+    test "extract as exactlyOne" <| fun _ ->
+        let child = [ Html.span []; Html.div [] ] 
+        let props = 
+            [
+                "children", box child
+            ]
+        let extractedProps, childOption = HtmlHelper.extractByKeyFast "children" props
+        Browser.Dom.console.log(extractedProps)
+        Browser.Dom.console.log(childOption)
+        expect(child).toBeTruthy()
+        let key, child =
+            match childOption with
+            | Some kvp -> kvp
+            | None -> failwith "Expected to find 'children' key"
+        expect(key).toBe("children")
+        expect(child).toEqual(child)
+        let propsContainChildren: bool = extractedProps |> Array.exists (fun (k, _) -> k = "children")
+        expect(propsContainChildren).toBeFalsy()
+        expect(extractedProps.Length).toBe((props |> Seq.length) - 1)