flutter_qjs

A quickjs engine for flutter.

Feature

This plugin is a simple js engine for flutter using the quickjs project with dart:ffi. Plugin currently supports all the platforms except web!

Event loop of FlutterQjs should be implemented by calling FlutterQjs.dispatch().

ES6 module with import function is supported and can be managed in dart with setModuleHandler.

A global function channel is presented to invoke dart function. Data conversion between dart and js are implemented as follow:

dart	js
Bool	boolean
Int	number
Double	number
String	string
Uint8List	ArrayBuffer
List	Array
Map	Object
JSFunction(...args) IsolateJSFunction(...args)	function(....args)
Future	Promise

notice: function can only be sent from js to dart. IsolateJSFunction always returns asynchronously.

Getting Started

Run on main thread

Create a FlutterQjs object, pass handlers to implement js-dart interaction and resolving modules. For example, you can use Dio to implement http in js:

final engine = FlutterQjs(
  methodHandler: (String method, List arg) {
    switch (method) {
      case "http":
        return Dio().get(arg[0]).then((response) => response.data);
      default:
        throw Exception("No such method");
    }
  },
  moduleHandler: (String module) {
    if(module == "hello")
      return "export default (name) => `hello \${name}!`;";
    throw Exception("Module Not found");
  },
);

in javascript, channel function is equiped to invoke methodHandler, make sure the second parameter is a list:

channel("http", ["http://example.com/"]);

import function is used to get modules:

import("hello").then(({default: greet}) => greet("world"));

notice: To use async function in module handler, try Run on isolate thread

Then call dispatch to dispatch event loop.

engine.dispatch();

Use evaluate to run js script, now you can use it synchronously, or use await to resolve Promise:

try {
  print(engine.evaluate(code ?? ''));
} catch (e) {
  print(e.toString());
}

Method close can destroy quickjs runtime that can be recreated again if you call evaluate.

Run on isolate thread

Create a IsolateQjs object, pass handlers to implement js-dart interaction and resolving modules. The methodHandler is used in isolate, so the handler function must be a top-level function or a static method. Async function such as rootBundle.loadString can be used now to get module:

dynamic methodHandler(String method, List arg) {
  switch (method) {
    case "http":
      return Dio().get(arg[0]).then((response) => response.data);
    default:
      throw Exception("No such method");
  }
}
final engine = IsolateQjs(
  methodHandler: methodHandler,
  moduleHandler: (String module) async {
    return await rootBundle.loadString(
        "js/" + module.replaceFirst(new RegExp(r".js$"), "") + ".js");
  },
);
// not need engine.dispatch();

Same as run on main thread, use evaluate to run js script. In this way, Promise return by evaluate will be automatically tracked and return the resolved data:

try {
  print(await engine.evaluate(code ?? '', "<eval>"));
} catch (e) {
  print(e.toString());
}

Method close can destroy quickjs runtime that can be recreated again if you call evaluate.

This example contains a complete demonstration on how to use this plugin.

For Mac & IOS developer

I am new to Xcode and iOS developing, and I cannot find a better way to support both simulators and real devices without combining the binary frameworks. To reduce build size, change the s.vendored_frameworks in ios/flutter_qjs.podspec to the specific framework.

For simulator, use:

s.vendored_frameworks = `build/Debug-iphonesimulator/ffiquickjs.framework`

For real device, use:

s.vendored_frameworks = `build/Debug-iphoneos/ffiquickjs.framework`

Two additional notes:

quickjs built with release config has bug in resolving Promise. Please let me know if you know the solution.
ios/make.sh limit the build architectures to avoid combine conflicts. Change the make.sh to support another architectures.

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