Fixes and features

- Change GetPageBuilder to WidgetCallback typedef, so we can use it outside Get and the name makes more sense.
- Added isDesktop/isMobile
- Added GetPlatform (web) getters to detect the OS it runs (using navigator UA)
- Added nil extension (can be useless now), to enforce the null type safety in JS for old dart2js versions (was undefined)

 import 'dart:math';
 import 'dart:ui' show lerpDouble;
+
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
@@ -7,6 +8,7 @@ import 'package:get/route_manager.dart';
 import 'package:get/src/core/get_main.dart';
 import 'package:get/src/instance/get_instance.dart';
 import 'package:get/utils.dart';
+
 import 'bindings_interface.dart';
 import 'custom_transition.dart';
 import 'default_transitions.dart';
@@ -41,7 +43,7 @@ class GetPageRoute<T> extends PageRoute<T> {
   @override
   final Duration transitionDuration;
 
-  final GetPageBuilder page;
+  final WidgetCallback page;
 
   final String routeName;
 

 import 'package:flutter/widgets.dart';
 import 'package:get/src/navigation/routes/bindings_interface.dart';
+
 import 'custom_transition.dart';
 import 'transitions_type.dart';
 
 class GetPage {
   final String name;
-  final GetPageBuilder page;
+  final WidgetCallback page;
   final bool popGesture;
   final Map<String, String> parameter;
   final String title;

@@ -18,4 +18,4 @@ enum Transition {
   native
 }
 
-typedef GetPageBuilder = Widget Function();
+typedef WidgetCallback = Widget Function();

 import 'dart:async';
+
 import 'package:flutter/widgets.dart';
+import 'package:get/src/navigation/routes/transitions_type.dart';
 import 'package:get/src/state_manager/rx/rx_interface.dart';
-import 'rx_impl.dart';
-
 
+import 'rx_impl.dart';
 
 /// The simplest reactive widget in GetX.
 ///
@@ -13,7 +14,7 @@ import 'rx_impl.dart';
 /// final _name = "GetX".obs;
 /// Obx(() => Text( _name.value )),... ;
 class Obx extends StatefulWidget {
-  final Widget Function() builder;
+  final WidgetCallback builder;
 
   const Obx(this.builder);
   _ObxState createState() => _ObxState();

 import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
-import 'package:flutter/foundation.dart';
+import 'package:get/get.dart';
 
 extension ContextExtensionss on BuildContext {
   /// The same of [MediaQuery.of(context).size]
@@ -117,8 +117,7 @@ extension ContextExtensionss on BuildContext {
     T watch,
   }) {
     double deviceWidth = mediaQuerySize.shortestSide;
-
-    if (kIsWeb) {
+    if (GetPlatform.isDesktop) {
       deviceWidth = mediaQuerySize.width;
     }
     if (deviceWidth >= 1200 && desktop != null) return desktop;

@@ -3,6 +3,12 @@ import '../regex/get_utils.dart';
 extension GetDynamicUtils on dynamic {
   /// It's This is overloading the IDE's options. Only the most useful and popular options will stay here.
 
+  /// In dart2js (in flutter v1.17) a var by default is undefined.
+  /// *Use this only if you are in version <- 1.17*.
+  /// So we assure the null type in json convertions to avoid the "value":value==null?null:value;
+  /// someVar.nil will force the null type if the var is null or undefined.
+  /// `nil` taken from ObjC just to have a shorter sintax.
+  dynamic get nil => GetUtils.nil(this);
   bool get isNull => GetUtils.isNull(this);
   bool get isNullOrBlank => GetUtils.isNullOrBlank(this);
 

@@ -8,4 +8,7 @@ class GetPlatform {
   static bool get isAndroid => GeneralPlatform.isAndroid;
   static bool get isIOS => GeneralPlatform.isIOS;
   static bool get isFuchsia => GeneralPlatform.isFuchsia;
+  static bool get isMobile => GetPlatform.isIOS || GetPlatform.isAndroid;
+  static bool get isDesktop =>
+      GetPlatform.isMacOS || GetPlatform.isWindows || GetPlatform.isLinux;
 }

@@ -8,4 +8,6 @@ class GeneralPlatform {
   static bool get isAndroid => Platform.isAndroid;
   static bool get isIOS => Platform.isIOS;
   static bool get isFuchsia => Platform.isFuchsia;
+  static bool get isDesktop =>
+      Platform.isMacOS || Platform.isWindows || Platform.isLinux;
 }

+// TODO: resolve platform/desktop by JS browser agent.
+// ignore: avoid_web_libraries_in_flutter
+import 'dart:html' as html;
+
+import 'package:get/utils.dart';
+
+html.Navigator _navigator = html.window.navigator;
+
 class GeneralPlatform {
   static bool get isWeb => true;
-  static bool get isMacOS => false;
-  static bool get isWindows => false;
-  static bool get isLinux => false;
-  static bool get isAndroid => false;
-  static bool get isIOS => false;
+
+  static bool get isMacOS =>
+      _navigator.appVersion.contains('Mac OS') && !GeneralPlatform.isIOS;
+
+  static bool get isWindows => _navigator.appVersion.contains('Win');
+
+  static bool get isLinux =>
+      (_navigator.appVersion.contains('Linux') ||
+          _navigator.appVersion.contains('x11')) &&
+      !isAndroid;
+
+  // @check https://developer.chrome.com/multidevice/user-agent
+  static bool get isAndroid => _navigator.appVersion.contains('Android ');
+
+  static bool get isIOS {
+    // maxTouchPoints is needed to separate iPad iOS13 vs new MacOS
+    return GetUtils.hasMatch(_navigator.platform, r'/iPad|iPhone|iPod/') ||
+        (_navigator.platform == 'MacIntel' && _navigator.maxTouchPoints > 1);
+  }
+
   static bool get isFuchsia => false;
+  static bool get isDesktop => isMacOS || isWindows || isLinux;
 }

@@ -2,6 +2,13 @@ class GetUtils {
   /// Checks if data is null.
   static bool isNull(dynamic s) => s == null;
 
+  /// In dart2js (in flutter v1.17) a var by default is undefined.
+  /// *Use this only if you are in version <- 1.17*.
+  /// So we assure the null type in json convertions to avoid the "value":value==null?null:value;
+  /// someVar.nil will force the null type if the var is null or undefined.
+  /// `nil` taken from ObjC just to have a shorter sintax.
+  static dynamic nil(dynamic s) => s == null ? null : s;
+
   /// Checks if data is null or blank (empty or only contains whitespace).
   static bool isNullOrBlank(dynamic s) {
     if (isNull(s)) return true;
@@ -475,4 +482,6 @@ class GetUtils {
 
   static bool hasMatch(String s, Pattern p) =>
       (s == null) ? false : RegExp(p).hasMatch(s);
+
+
 }