js: auto-generate getters and setters for calls to MakeWrapper

myitcv · myitcv · commit 5a7149a7a04b · 2018-04-14T00:03:29.000+01:00
Currently the documentation for js.MakeWrapper is:

"MakeWrapper creates a JavaScript object which has wrappers for the
exported methods of i. Use explicit getter and setter methods to expose
struct fields to JavaScript."

Where the value passed to MakeWrapper is a struct value (or more
interestingly a pointer to a struct value) we can actually
auto-generate getters and setters in the Javascript world, rather than
requiring explicit getters and setters to be defined on the Go side.
diff --git a/js/js.go b/js/js.go
@@ -144,6 +144,29 @@ func MakeWrapper(i interface{}) *Object {
 			return Global.Call("$externalizeFunction", v.Get(m.Get("prop").String()), m.Get("typ"), true).Call("apply", v, args)
 		})
 	}
+	fields := v.Get("constructor").Get("fields")
+	if fields == Undefined {
+		if e := v.Get("constructor").Get("elem"); e != Undefined {
+			fields = e.Get("fields")
+		}
+	}
+	if fields != Undefined {
+		for i := 0; i < fields.Length(); i++ {
+			f := fields.Index(i)
+			if !f.Get("exported").Bool() {
+				continue
+			}
+			op := Global.Get("Object").New()
+			op.Set("get", func() *Object {
+				return Global.Call("$externalize", v.Get("$val").Get(f.Get("prop").String()), f.Get("typ"))
+			})
+			op.Set("set", func(jv *Object) {
+				gv := Global.Call("$internalize", jv, f.Get("typ"))
+				v.Get("$val").Set(f.Get("prop").String(), gv)
+			})
+			Global.Get("Object").Call("defineProperty", o, f.Get("prop"), op)
+		}
+	}
 	return o
 }
 
diff --git a/js/js_test.go b/js/js_test.go
@@ -423,6 +423,8 @@ func TestMakeFunc(t *testing.T) {
 }
 
 type M struct {
+	Name string
+
 	f int
 }
 
@@ -436,7 +438,7 @@ func (m *M) Method(a interface{}) map[string]string {
 }
 
 func TestMakeWrapper(t *testing.T) {
-	m := &M{42}
+	m := &M{f: 42}
 	if !js.Global.Call("eval", `(function(m) { return m.Method({x: 1})["y"] === "z"; })`).Invoke(js.MakeWrapper(m)).Bool() {
 		t.Fail()
 	}
@@ -453,6 +455,21 @@ func TestMakeWrapper(t *testing.T) {
 	js.Global.Call("eval", `(function(f, m) { f(m); })`).Invoke(f, js.MakeWrapper(m))
 }
 
+func TestMakeWrapperFields(t *testing.T) {
+	want := "Gopher"
+	m := &M{Name: want}
+	o := js.MakeWrapper(m)
+	js.Global.Set("banana", o)
+	if got := js.Global.Call("eval", `(function(o) { return o["banana"].Name; })`).Invoke(js.Global).String(); got != want {
+		t.Fatalf("wanted %v; got %v", want, got)
+	}
+	want = "JS"
+	js.Global.Call("eval", `(function(o) { o["banana"].Name = "`+want+`"; })`).Invoke(js.Global)
+	if got := m.Name; got != want {
+		t.Fatalf("wanted %v; got %v", want, got)
+	}
+}
+
 func TestCallWithNull(t *testing.T) {
 	c := make(chan int, 1)
 	js.Global.Set("test", func() {
