Fix invalid comparison to js.Undefined() in go1.14.

Author: janpfeifer

core/js/js.go

@@ -198,6 +198,11 @@ func (v Value) Invoke(args ...interface{}) Value {
 	panic(message)
 }
 
+// IsUndefined reports whether v is the JavaScript value "undefined".
+func (v Value) IsUndefined() bool {
+	panic(message)
+}
+
 // JSValue implements Wrapper interface.
 func (v Value) JSValue() Value {
 	panic(message)

dom/helper.go

@@ -7,13 +7,13 @@ import js "github.com/gowebapi/webapi/core/js"
 // accound
 func (t *Element) RequestFullscreenByBrowser() {
 	elem := t.Value_JS
-	if elem.Get("requestFullscreen") != js.Undefined() {
+	if !elem.Get("requestFullscreen").IsUndefined() {
 		elem.Call("requestFullscreen", "")
-	} else if elem.Get("mozRequestFullScreen") != js.Undefined() { /* Firefox */
+	} else if !elem.Get("mozRequestFullScreen").IsUndefined() { /* Firefox */
 		elem.Call("mozRequestFullScreen", "")
-	} else if elem.Get("webkitRequestFullscreen") != js.Undefined() { /* Chrome, Safari and Opera */
+	} else if !elem.Get("webkitRequestFullscreen").IsUndefined() { /* Chrome, Safari and Opera */
 		elem.Call("webkitRequestFullscreen", "")
-	} else if elem.Get("msRequestFullscreen") != js.Undefined() { /* IE/Edge */
+	} else if !elem.Get("msRequestFullscreen").IsUndefined() { /* IE/Edge */
 		elem.Call("msRequestFullscreen", "")
 	}
 }