Use commonjs module

[budziam]

This PR solves issue with using vuex-class-modules along with jest testing framework. Unfortunately Jest does not play well with ES6 module syntax. You can read more here: jestjs/jest#2550 (comment)

I think it's common approach to use commonjs module instead of es6 one.

[bodograumann]

The way I read that jest comment, you can “simply” transpile on your side.
I’m not convinced about switching to commonjs2, because we would loose tree-shaking. This might currently not be a big problem, but if the library grows in the future it will be.
At least we should provide a commonjs2 as well as an esm build.

[budziam]

So how about providing two builds? Can you do it?

[bodograumann]

Should be possible, in principle. My first instinct would be to add a rollup build-step. Not sure if I can find the time right now to flesh it out properly though.

[bodograumann]

Could you please check if this works for you: https://github.com/gertqin/vuex-class-modules/tree/feature/commonjs ?
I think you need to require("vuex-class-modules/dist").

[budziam]

There is one problem left. Typings are saved in lib directory. As a result, when using vuex-class-modules/dist, typescript does not see proper typings

Directory structure looks as follow:

[bodograumann]

That is true. I have switched to rollup-plugin-typescript2 because it generates the declaration files automatically.
In order to have no duplicate files, I moved the commonjs variant to lib/index.common.js. There was no lib/index.common.d.ts generated however. Not sure if that is a problem.
Please try it out. If the declarations are not found, could you also try to copy lib/index.d.ts to lib/index.common.d.ts please?

[gertqin]

Closing this in favor of #46