Typescript is Javascript + types, so the code itself is Javascript and you have an additional syntax for declaring types. It's also recommended to add ESLint into the mix.
For example this JS code:
https://gist.github.com/quochuy/01d9e0f7cd56797b85e531ee984975ef
Would be come this in Typescript:
https://gist.github.com/quochuy/328a0e93005dabf0d015819bc9c13840
Or this in JS:
https://gist.github.com/quochuy/42c980e74e5c80a6a94548f282688560
Becomes this in TS:
https://gist.github.com/quochuy/5b95ba862fb6dc5d534b0c8a1c0658af