Add (*js.Value).InstanceOf()

js/js_notwasm.go

@@ -63,12 +63,14 @@ type Value struct {
 }
 
 var (
-	id *js.Object
+	id         *js.Object
+	instanceOf *js.Object
 )
 
 func init() {
 	if js.Global != nil {
 		id = js.Global.Call("eval", "(function(x) { return x; })")
+		instanceOf = js.Global.Call("eval", "(function(x, y) { return x instanceof y; })")
 	}
 }
 
@@ -171,6 +173,10 @@ func (v Value) String() string {
 	return v.v.String()
 }
 
+func (v Value) InstanceOf(t Value) bool {
+	return instanceOf.Invoke(v, t).Bool()
+}
+
 func GetInternalObject(v Value) interface{} {
 	return v.v
 }

js/js_test.go

@@ -64,3 +64,12 @@ func TestInt64(t *testing.T) {
 		t.Errorf("got %#v, want %#v", got, want)
 	}
 }
+
+func TestInstanceOf(t *testing.T) {
+	arr := js.Global.Call("eval", "[]")
+	got := arr.InstanceOf(js.Global.Call("eval", "Array"))
+	want := true
+	if got != want {
+		t.Errorf("got %#v, want %#v", got, want)
+	}
+}