These tests and their files are written in TypeScript, but you don't even need to know TypeScript to use them. The functions are already set up with the needed declarations. All you need to do is fill them in to make them pass the tests.
The tests are set up to fail fast, meaning as soon as one test fails no other tests after it run. This is meant to help you keep focused the current test at hand.
It's really this simple!
git clone git@github.com:TSiege/Tech-Interview-Cheat-Sheet.git
cd ./Tech-Interview-Cheat-Sheet/challenges/typescript
npm install
npm test