How could I include a plugin system for my Dart app? - plugins

Question

I have a Qt application containing a Webkit module and using Dart (compiled to JS). It's like a bare-bones browser written in Qt. The application basically replaces certain text on the webpage with different text. I want users to be able to make their own Dart files to replace their own text with their own different text.
Any recommendations for approaches to creating a plugin system?

Answer 1

I think that this question needs a little clarification: are you asking about using Dart for scripting Qt applications (where Dart plays the role of a scripting language), or are you asking about a plugin system for Dart application that is compiled to JS and used in a Qt application, probably via QtScript (in which case, the role of a scripting language is played by JavaScript)?
I presume that it is the latter variant (and I don't know enough about Qt to be able to answer about the former variant anyway).
Let's assume that all plugins for the Dart application are available at the build time of that Qt application, so that you don't need to compile Dart to JS dynamically. Then, if you compile a Dart script, resulting JS will include all necessary code from its #imports. All you need is to create a proper script that imports all plugins and calls them (importing isn't enough, as dead code will be eliminated).
Maybe an example will be more instructive. Let's say that you want to allow plugins to do some work on a web page. One way you might structure it is that every plugin will be a separate #library with a top-level function of a well known name (say doWork). Example of a plugin:
// my_awesome_plugin.dart
#library('My Awesome Plugin')
doWork(page) {
page.replaceAll('JavaScript is great', 'Dart is great');
}
You can have as many plugins of this nature as you wish. Then, you would (at the build time) generate a following simple main script in Dart:
// main.dart
// these lines are automatically generated -- for each plugin file,
// one #import with unique prefix
#import('my_awesome_plugin.dart', prefix: 'plugin1');
#import('another_plugin.dart', prefix: 'plugin2');
main() {
var page = ...; // provided externally, from your Qt app
// and these lines are automatically generated too -- for each plugin,
// call the doWork function (via the prefix)
plugin1.doWork(page);
plugin2.doWork(page);
}
Then, if you compile main.dart to JavaScript, it will include all those plugins.
There are other possibilities to structure the plugin system: each plugin could be a class implementing a specific interface (or inheriting from a specific base class), but the general approach would be the same. At least the approach that I would recommend -- making each plugin a separate library.
You probably don't like the step with generating the main script automatically, and I don't like it either. But currently, Dart only allows one way to dynamically load new code: spawning new isolates. I'm not sure how (or even if) that would work in QtScript, because isolates are implemented as web workers when compiled to JavaScript, so I won't discuss this here.
Things will get more complicated if you want to support compiling Dart scripts at the runtime of your Qt application, but I think that I'm already guessing too much about your project and I might be writing about something you don't really need. So I'll finish it like this for now.