feature: synchronous communication with dart from javascript

[Tiagoperes]

Related issues

#53

Description

The javascript code calls the Dart code via the function sendMessage. Dart listens to these messages via javascriptRuntime.onMessage(channelName, callback).

The problem is: the function provided to callback has the return type of void, i.e. the JS code can call dart, but it cannot get a return value.

From the JS code, if we call:

const result = sendMessage(channelName);

Then result should get the return value of the message handler, written in Dart.

There are workarounds for this problem, but I can't think of any that doesn't involve transforming the JS code into async, which can not be viable in some cases. Furthermore, any solution other than having a return value for sendMessage will be more complicated than it should be.

@LucaBoss74 added support for this on QuickJS in #54, but it still didn't work for JavascriptCore. Also, the callback for onMessage had void as a return type when it should be dynamic.

This PR changes the return type of onMessage to dynamic and includes support for returning values from message events on JavascriptCore.

I think with this PR the full support for this feature should be ready. @abner can you check please if what I did is correct? This is the first time I mess with dart:ffi and I might have overlooked something.

Tested with Android (forceJavascriptCoreOnAndroid: true) and iOS.

[abner]

Hi @Tiagoperes, thanks for the Pull Request. I will check it and would merge if it is OK.

Related issues

#53

Description

The javascript code calls the Dart code via the function sendMessage. Dart listens to these messages via javascriptRuntime.onMessage(channelName, callback).

The problem is: the function provided to callback has the return type of void, i.e. the JS code can call dart, but it cannot get a return value.

From the JS code, if we call:

const result = sendMessage(channelName);

Then result should get the return value of the message handler, written in Dart.

There are workarounds for this problem, but I can't think of any that doesn't involve transforming the JS code into async, which can not be viable in some cases. Furthermore, any solution other than having a return value for sendMessage will be more complicated than it should be.

@LucaBoss74 added support for this on QuickJS in #54, but it still didn't work for JavascriptCore. Also, the callback for onMessage had void as a return type when it should be dynamic.

This PR changes the return type of onMessage to dynamic and includes support for returning values from message events on JavascriptCore.

I think with this PR the full support for this feature should be ready. @abner can you check please if what I did is correct? This is the first time I mess with dart:ffi and I might have overlooked something.

Tested with Android (forceJavascriptCoreOnAndroid: true) and iOS.