update README

README.md

@@ -1,18 +1,48 @@
+<!--
+ * @Description: 
+ * @Author: ekibun
+ * @Date: 2020-08-08 08:16:50
+ * @LastEditors: ekibun
+ * @LastEditTime: 2020-08-20 00:33:22
+-->
 # flutter_qjs
 
 A quickjs engine for flutter.
 
+## Feature
+
+This plugin is a simple js engine for flutter used `quickjs` project.
+
+Each `FlutterJs` object create a new thread that running a simple js loop. A global async function `dart` is presented to invoke dart function, and `Promise` is supported in evaluating js script so that you can use `await` or `then` to get external result from `dart`. 
+
+Data convertion between dart and js are implemented as follow:
+
+| dart | js |
+| --- | --- |
+| Bool | boolean |
+| Int | number |
+| Double | number |
+| String | string |
+| Uint8List/Int32List/Int64List | ArrayBuffer |
+| Float64List | number[] |
+| List | Array |
+| Map | Object |
+| Closure(List) => Future | function(....args) |
+
+**notice:**
+1. All the `Uint8List/Int32List/Int64List` sent from dart will be converted to `ArrayBuffer` without marked the size of elements, and the `ArrayBuffer` will be converted to `Uint8List`.
+
+2. `function` can only sent from js to dart and all the arguments will be packed in a dart `List` object.
+
 ## Getting Started
 
-This project is a starting point for a Flutter
-[plug-in package](https://flutter.dev/developing-packages/),
-a specialized package that includes platform-specific implementation code for
-Android and/or iOS.
+1. Creat a `FlutterJs` object. Makes sure call `close` to release memory when not need it.
 
-For help getting started with Flutter, view our
-[online documentation](https://flutter.dev/docs), which offers tutorials,
-samples, guidance on mobile development, and a full API reference.
+2. Call `setMethodHandler` to maintain `dart` function.
 
-The plugin project was generated without specifying the `--platforms` flag, no platforms are currently supported.
-To add platforms, run `flutter create -t plugin --platforms <platforms> .` under the same
-directory. You can also find a detailed instruction on how to add platforms in the `pubspec.yaml` at https://flutter.dev/docs/development/packages-and-plugins/developing-packages#plugin-platforms.
+3. Use `evaluate` to evaluate js script. Makes sure surrounding try-cacth to capture evaluating error.
+
+[this](example/lib/test.dart) contains a fully use of this plugin. 
+
+**notice:**
+To use this plugin in Linux desktop application, you must change `cxx_std_14` to `cxx_std_17` in your project's `CMakeLists.txt`.