syscall/js: rename Callback.Close to Release and expose Callback.Value

This makes Callback more in line with TypedArray. The name "Release" is
better than "Close" because the function does not implement io.Closer.

Change-Id: I23829a14b1c969ceb04608afd9505fd5b4b0df2e
Reviewed-on: https://go-review.googlesource.com/121216
Run-TryBot: Richard Musiol <neelance@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/roundtrip_js.go

@@ -110,7 +110,7 @@ func (t *Transport) RoundTrip(req *Request) (*Response, error) {
 		case <-req.Context().Done():
 		}
 	})
-	defer success.Close()
+	defer success.Release()
 	failure := js.NewCallback(func(args []js.Value) {
 		err := fmt.Errorf("net/http: fetch() failed: %s", args[0].String())
 		select {
@@ -118,7 +118,7 @@ func (t *Transport) RoundTrip(req *Request) (*Response, error) {
 		case <-req.Context().Done():
 		}
 	})
-	defer failure.Close()
+	defer failure.Release()
 	respPromise.Call("then", success, failure)
 	select {
 	case <-req.Context().Done():
@@ -171,7 +171,7 @@ func (r *streamReader) Read(p []byte) (n int, err error) {
 			a.Release()
 			bCh <- value
 		})
-		defer success.Close()
+		defer success.Release()
 		failure := js.NewCallback(func(args []js.Value) {
 			// Assumes it's a TypeError. See
 			// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError
@@ -180,7 +180,7 @@ func (r *streamReader) Read(p []byte) (n int, err error) {
 			// the read method.
 			errCh <- errors.New(args[0].Get("message").String())
 		})
-		defer failure.Close()
+		defer failure.Release()
 		r.stream.Call("read").Call("then", success, failure)
 		select {
 		case b := <-bCh:
@@ -234,7 +234,7 @@ func (r *arrayReader) Read(p []byte) (n int, err error) {
 			a.Release()
 			bCh <- value
 		})
-		defer success.Close()
+		defer success.Release()
 		failure := js.NewCallback(func(args []js.Value) {
 			// Assumes it's a TypeError. See
 			// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError
@@ -242,7 +242,7 @@ func (r *arrayReader) Read(p []byte) (n int, err error) {
 			// See https://fetch.spec.whatwg.org/#concept-body-consume-body for reasons this might error.
 			errCh <- errors.New(args[0].Get("message").String())
 		})
-		defer failure.Close()
+		defer failure.Release()
 		r.arrayPromise.Call("then", success, failure)
 		select {
 		case b := <-bCh:

src/syscall/js/callback.go

@@ -46,8 +46,8 @@ var (
 // A Callback can be passed to functions of this package that accept interface{},
 // for example Value.Set and Value.Call.
 type Callback struct {
+	Value // the JavaScript function that queues the callback for execution
 	id    uint32
-	enqueueFn Value // the JavaScript function that queues the callback for execution
 }
 
 // NewCallback returns a wrapped callback function. It can be passed to functions of this package
@@ -59,7 +59,7 @@ type Callback struct {
 // As a consequence, if one callback blocks this goroutine, other callbacks will not be processed.
 // A blocking callback should therefore explicitly start a new goroutine.
 //
-// Callback.Close must be called to free up resources when the callback will not be used any more.
+// Callback.Release must be called to free up resources when the callback will not be used any more.
 func NewCallback(fn func(args []Value)) Callback {
 	callbackLoopOnce.Do(func() {
 		go callbackLoop()
@@ -71,8 +71,8 @@ func NewCallback(fn func(args []Value)) Callback {
 	callbacks[id] = fn
 	callbacksMu.Unlock()
 	return Callback{
+		Value: makeCallbackHelper.Invoke(id, pendingCallbacks, resolveCallbackPromise),
 		id:    id,
-		enqueueFn: makeCallbackHelper.Invoke(id, pendingCallbacks, resolveCallbackPromise),
 	}
 }
 
@@ -95,17 +95,19 @@ func NewEventCallback(flags EventCallbackFlag, fn func(event Value)) Callback {
 		fn(args[0])
 	})
 	return Callback{
-		id: c.id,
-		enqueueFn: makeEventCallbackHelper.Invoke(
+		Value: makeEventCallbackHelper.Invoke(
 			flags&PreventDefault != 0,
 			flags&StopPropagation != 0,
 			flags&StopImmediatePropagation != 0,
 			c,
 		),
+		id: c.id,
 	}
 }
 
-func (c Callback) Close() {
+// Release frees up resources allocated for the callback.
+// The callback must not be invoked after calling Release.
+func (c Callback) Release() {
 	callbacksMu.Lock()
 	delete(callbacks, c.id)
 	callbacksMu.Unlock()

src/syscall/js/js.go

@@ -99,7 +99,7 @@ func ValueOf(x interface{}) Value {
 	case TypedArray:
 		return x.Value
 	case Callback:
-		return x.enqueueFn
+		return x.Value
 	case nil:
 		return valueNull
 	case bool:

src/syscall/js/js_test.go

@@ -214,7 +214,7 @@ func TestCallback(t *testing.T) {
 		}
 		c <- struct{}{}
 	})
-	defer cb.Close()
+	defer cb.Release()
 	js.Global().Call("setTimeout", cb, 0, 42)
 	<-c
 }
@@ -234,10 +234,10 @@ func TestEventCallback(t *testing.T) {
 		cb := js.NewEventCallback(flags, func(event js.Value) {
 			c <- struct{}{}
 		})
-		defer cb.Close()
+		defer cb.Release()
 
 		event := js.Global().Call("eval", fmt.Sprintf("({ called: false, %s: function() { this.called = true; } })", name))
-		js.ValueOf(cb).Invoke(event)
+		cb.Invoke(event)
 		if !event.Get("called").Bool() {
 			t.Errorf("%s not called", name)
 		}
@@ -250,7 +250,7 @@ func ExampleNewCallback() {
 	var cb js.Callback
 	cb = js.NewCallback(func(args []js.Value) {
 		fmt.Println("button clicked")
-		cb.Close() // close the callback if the button will not be clicked again
+		cb.Release() // release the callback if the button will not be clicked again
 	})
 	js.Global().Get("document").Call("getElementById", "myButton").Call("addEventListener", "click", cb)
 }