Add TypeScript typings

[frenzzy]

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

Closes #101

@pradyuman, @dangmai, @anantoghosh, @gytisgreitai, @jtmthf, @tlaziuk, @Lodin would be cool if some of you guys could take a look, thanks in advance!

[codecov-io]

Codecov Report

Merging #159 into master will not change coverage. The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #159   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           4      4           
  Lines         144    144           
  Branches       42     42           
=====================================
  Hits          144    144

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[gytisgreitai]

Well I'm a bit out of Typescript world, so some of those maybe rookie mistakes.

I've replaced version in package.json with "git+https://github.com/frenzzy/universal-router.git#54e8b4047b987a1e7d75f7e3a1588c02ea31e2a0" and here are some observations:

1. VSCode compiles fine, shows bindings all ok
2. yarn start when using react-scripts-ts fails with Module not found: Can't resolve 'universal-router'
3. How do I do imports with default class export ? E.g. now I'm doing, is there a prettier way?:

   import UniversalRouter from 'universal-router';
   import { Route, Context } from 'universal-router';

4. In Route the action param signature is as follows:

   action?: (context: RouteContext<C, R> & C, params: Params) => R | Promise<R> | void

shouldn't context be optional? cause I can simply do action: () => (<Dashboard/>) and it does seem to work

[frenzzy]

Hey @gytisgreitai, thanks for your feedback!

1. Cool! This is the main goal why I want to add typings to the package.
2. The package requires compilation before usage, it is why you can't just use git url. Instead you have to do the following:

   git clone https://github.com/frenzzy/universal-router.git
   cd universal-router
   git checkout typescript
   yarn install
   yarn build
   cd dist
   yarn link
   cd ../../your-project-name
   yarn link universal-router
   yarn start

3. Like this:

   import UniversalRouter, { Route, Context } from 'universal-router';

4. From TypeScript docs:

Optional Parameters in Callbacks

Don’t use optional parameters in callbacks unless you really mean it:

/* WRONG */
interface Fetcher {
    getObject(done: (data: any, elapsedTime?: number) => void): void;
}

This has a very specific meaning: the done callback might be invoked with 1 argument or might be invoked with 2 arguments. The author probably intended to say that the callback might not care about the elapsedTime parameter, but there’s no need to make the parameter optional to accomplish this – it’s always legal to provide a callback that accepts fewer arguments.

Do write callback parameters as non-optional:

/* OK */
interface Fetcher {
    getObject(done: (data: any, elapsedTime: number) => void): void;
}