add typescript dependency

[technicallyjosh]

Per depcheck, if you have TypeScript installed as a dependency, it works on TypeScript files.

This should resolve some issues such as:

• Fails to find usage of any of the modules #311
• Support for import star syntax #339
• False positives given #313

[LinusU]

Hmm, so I thought that it would pick up the local dependency on TypeScript 🤔

The only problem with this is that it will always use the TypeScript version that we define, instead of using the same as the package that is being checked...

Not sure if that is a big deal though 🤔

[technicallyjosh]

It's up to you guys if you want to include it by default. I figured I'd make it a non issue since it's a dependency that requires it to be installed. Perhaps adding docs might be just as good of a fix to let people know to do an npm i -g npm-check typescript if they want TypeScript files included. 🤷‍♂

[Artoria2e5]

It can be made a "peer" dependency or put in optionalDependencies.

[newlukai]

I find it quite difficult to get information on how to let npm-check know that my project uses TypeScript. I hope that globally installing TypeScript is not the only way.
I'm working on several projects using different TypeScript versions and it's not feasible for me to install TypeScript globally. Additionally I don't want to bring TypeScript to production, so I usually include TypeScript as devDependency.
And it seems that doesn't work for npm-check.

[newlukai]

I noticed that my issues regarding TypeScript were fixed after updating the depcheck dependency. Thus I added a PR.
But I also noticed that the latest commit was to downgrade depcheck in order to restore compatibility with older Node versions.
So are we in a quandary now?

[technicallyjosh]

I don't use the lib anymore and this is super stale. 😅