'Type not assignable...' when not supplying every option parameter to constructor when using TypeScript JS file checking

[luke-m]

We're using TypeScript with JS file checking enabled in our project. What that means is that TypeScript will check JS files for JSDoc definitions and interpret them as types.
scrollbooster's index file contains JSDocs definitions:

When I try to create a new ScrollBooster instance with the same options as suggested in the README.md like this:

new ScrollBooster({
    viewport: document.querySelector('.viewport'),
    scrollMode: 'transform'
});

... TypeScript complains about missing parameters:

TS2345: Argument of type '{ viewport: HTMLElement; scrollMode: string; }' is not assignable to parameter of type '{ viewport: Element; content: Element; direction: string; pointerMode: string; scrollMode: string; bounce: boolean; bounceForce: number; friction: number; textSelection: boolean; ... 5 more ...; shouldScroll: Function; }'.
  Type '{ viewport: HTMLElement; scrollMode: string; }' is missing the following properties from type '{ viewport: Element; content: Element; direction: string; pointerMode: string; scrollMode: string; bounce: boolean; bounceForce: number; friction: number; textSelection: boolean; ... 5 more ...; shouldScroll: Function; }': content, direction, pointerMode, bounce, and 9 more.

That's because in the JSDocs comments of ScrollBooster's index file, non-essential parameters are not marked as optional. In JSDocs, you can mark parameters as optional by wrapping the parameter name in brackets ( [] ). When I do that for all the non-essential parameters, TypeScript stops complaining and my example works 🎉 .

@ilyashubin I wanted to open a PR, but I can't seem to create a branch for this repo.