Does JavaScriptEngineFactory.cs really need a dependency on V8 or Chakra?

[JoshuaKGoldberg]

Deploying multiple JS engine DLLs is a pain and extra time taken during server deployments. V8 in particular has a few DLL dependencies and can become DLL hell.

In setting up ReactJS.NET with a server, I ended up wanting to both set up my own container registrations and only ever use the Chakra engine. Here's the code it ended up with:

var container = AssemblyRegistration.Container;
var fileSystem = new SimpleFileSystem();

var msIeEngineFactory = new MsieJsEngineFactory();
JsEngineSwitcher.Instance.EngineFactories.Add(msIeEngineFactory);
JsEngineSwitcher.Instance.DefaultEngineName = "MsieJsEngine";

var engineFactory = new JavaScriptEngineFactory(
    JsEngineSwitcher.Instance,
    ReactSiteConfiguration.Configuration,
    fileSystem);

container.Register<IReactSiteConfiguration>((c, o) => ReactSiteConfiguration.Configuration);
container.Register<ICache, NullCache>();
container.Register<IFileCacheHash, FileCacheHash>().AsPerRequestSingleton();
container.Register<FileCacheHash, FileCacheHash>().AsPerRequestSingleton();
container.Register<IFileSystem, SimpleFileSystem>(fileSystem);
container.Register<JsEngineSwitcher>((c, o) => JsEngineSwitcher.Instance);
container.Register<IJavaScriptEngineFactory>(engineFactory);
container.Register<IReactEnvironment, ReactEnvironment>().AsPerRequestSingleton();
container.Register<ReactEnvironment, ReactEnvironment>().AsPerRequestSingleton();

ReactSiteConfiguration.Configuration
    .SetLoadBabel(false)
    .AddScriptWithoutTransform("local/Wat.js");

The JavaScriptEngineFactory call loads JavaScriptEngineFactory.cs, which has a dependency on JavaScriptEngineSwitcher.V8 or JavaScriptEngineSwitcher.ChakraCore:

#if NET40
using JavaScriptEngineSwitcher.V8;
#else
using JavaScriptEngineSwitcher.ChakraCore;
#endif

That means if you want to load that file, you have to load whichever engine switcher DLL is tied to your .NET version. Eww! In order to avoid having to figure out V8 deployments, I ended up copy & pasting JavaScriptEngineFactory into a new file and removing the references to V8. Forking is bad and I feel bad.

A better solution IMO would be to only load the DLLs deemed necessary. How about JavaScriptEngineFactory take in some sort of new IJavaScriptEngineProvider(s) via dependency injection? That way we can skip loading the V8 or Chakra DLLs unless necessary. It would also help remove some of the logic for switching between the two in the class itself, which as it stands now seems like a weird responsibility for the class to have.

[Daniel15]

. How about JavaScriptEngineFactory take in some sort of new IJavaScriptEngineProvider(s) via dependency injection?

You're right. I think we can totally drop the hard dependency on V8 / ChakraCore and instead rely on people to manually configure JavaScriptEngineSwitcher, like you did:

JsEngineSwitcher.Instance.EngineFactories.Add(msIeEngineFactory);
JsEngineSwitcher.Instance.DefaultEngineName = "MsieJsEngine";

This became a lot easier to do in JavaScriptEngineSwitcher v2.

Of course this means that it needs a bit more configuration rather than mostly working out-of-the-box, but perhaps that's worth it?

[JoshuaKGoldberg]

Of course this means that it needs a bit more configuration rather than mostly working out-of-the-box, but perhaps that's worth it?

Maybe. Similar to the existing logic, can it try at runtime to load the .NET-version-appropriate DLL as needed?

[roman-yagodin]

I think we can totally drop the hard dependency on V8 / ChakraCore and instead rely on people to manually configure JavaScriptEngineSwitcher.

I vote for this with both my hands!

[dustinsoftware]

@roman-yagodin @JoshuaKGoldberg support for this is shipped in the 4.0.0 rc