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:
Would be come this in Typescript:
~~~ embed:328a0e93005dabf0d015819bc9c13840 gist metadata:cXVvY2h1eS8zMjhhMGU5MzAwNWRhYmYwZDAxNTgxOWJjOWMxMzg0MA== ~~~
Or this in JS:
Becomes this in TS:
~~~ embed:5b95ba862fb6dc5d534b0c8a1c0658af gist metadata:cXVvY2h1eS81Yjk1YmE4NjJmYjZkYzVkNTM0YjBjOGExYzA2NThhZg== ~~~