A bit of a story on why we are moving from Jurassic to Edge.js

In a project I’m working on we have plenty of shared logic that we want to execute both on client and server. We decided that we want it to be written in JavaScript. As our backend is .NET we used Jurassic library to compile JavaScript code on the server and then to execute it whenever we needed it. We used Jurassic library for quite some time and it worked fine. It is a bit slow on doing initial compile of all of our JS code, so our startup time lagged (+30 sec or so). Execution time also wished to be better. But recently we started to get crashes that seemed to be from the library itself, but it is a real pain to find out what was the problem since library doesn’t provide JS stack trace.

How to integrate Edge.js in C# project

If everything goes smoothly all you need to do is to reference EdgeJs.dll through NuGet and execute your node script using Edge.Func. But life is not that easy.

I would recommend to create minimalistic project with basic things that are used in the project you are going to integrate Edge into. This will allow you to save time on testing how integration works. You can start with hello world available on Edge.js page. I’ve also created simple project with few things I wanted to test out, mainly loading of modules, passing-in and getting results.

Here below are three files from my sample project. It should be easy to follow the code plus there are some comments just below the code.

In Program.cs you can see how easy it is to invoke Edge and pass in a dynamic object. Getting result back is also super easy. If you are working with large objects you might want to convert the object to JSON and then pass it into your JavaScript. This is what we do using Newtonsoft.Json.

Edge.Func has to accept a function of a specific signature with a callback being called. Alternatively you can have a module that itself is a function and then load it. Exactly what I did with module edgeEntryPoint.js. To do something useful, I’m trying to dynamically find an object ‘className’ and call a function ‘functionName’ on it plus I send some other parameters. This is somewhat similar to what we want to achieve in our project.

calc2D.js is a module with logic that I’m trying to call. There is one interesting thing about it. It is the way how it exposes itself to the world. It checks if there is ‘window’ and assigns itself to it or otherwise assigns itself to ‘GLOBAL’ so this module with work fine both in browser and in Node.js.

Few things that could go wrong

Signing

It is very likely that you are signing your assemblies therefore you will get compile error telling you:

Assembly generation failed — Referenced assembly ‘Edge’ does not have a strong name.

Don’t panic. You can still sign Edge.dll. There are few ways of doing it. You can even rebuild Edge source code with your key.snk or what I find more easier is to disassemble, rebuild and sign from VS console using 2 commands:

ildasm /all /out=Edge.il Edge.dll

ilasm /dll /key=key.snk Edge.il

window is not defined

In case if you want to run same JavaScript both on client and on server you might run into issues of namespacing and global variables. Above I’ve already demonstrated how we exposed our own namespace by checking if ‘window’ is defined. If you are trying to load a lot of modules you might want to assign them to global variables before your callback function returns. For example:

moment = require(‘../../moment.js’);

If you still get error ‘window is not defined’ it could be that some internal logic is relying on global ‘window’ being defined somewhere. In order to fix it you can just have this kind of a hack in front of your entry function:

GLOBAL.window = GLOBAL;

Edge.Func hangs

There is already issue reported on this on GitHub edge#215, which I believe is similar to what we are experiencing (if not exactly same).

In our case we want to run JavaScript from .NET that runs in IIS. I created wrapper around Edge that keeps compiled function, and then Invoking is done whenever we need it. One interesting thing started to happen when I had web site pointing to bin folder. After rebuilding the app initialization would hang on Edge.Func. If I kill the w3wp.exe process and start the app from scratch all works just fine. Unfortunately I was not able to reproduce this with console application. I suspect that this has something to do with how IIS threads run and possibly locks files, but still if I locked node.dll, double_edge.js and edge.node files for console app it was not reproducible.
Issue was solved by ensuring that IIS is stopped before building the web project. This can be achieved by using commands ‘iisreset /stop’ and ‘iisreset /start’ in BeforeBuild and AfterBuild tags of your csproj file.
I don’t think that this is the best way to solve this or that running Edge.js in IIS is very reliable, so I spent a bit of time reading source code of Edge.js and debugging it. And to be honest I don’t quite understand all the things around invoking native code to make all this magic happen. Because of this I’m not 100% sure that entire solution with Edge.js will prove itself to be a decent one.

All in all Edge.js is a really great tool. Not so long ago things it does would be unbelievably difficult to achieve.

I hope this post is of some help to you.