Add scroll-promises examples

[chrisdavidmills]

In Chrome 150 onwards, the standard Element and Window scroll methods now return promises. See https://chromestatus.com/feature/5082138340491264. This is particularly useful when a scroll operation is not instantaneous (e.g. you've got scroll-behavior: smooth; set on the scrolling container), and you want to programmatically react to the scroll operation finishing, for example, by updating the UI.

Affected methods are:

• Element.scroll()
• Element.scrollBy()
• Element.scrollIntoView()
• Element.scrollTo()
• Window.scroll()
• Window.scrollBy()
• Window.scrollTo()

This PR adds a couple of demos that show each promise-returning scroll method in use. I could do these as live examples, but I decided not to, as I don't want to add a huge standalone live example to all seven pages, with all of them doing nearly the same thing. I'd rather provide a couple of code snippets on each page and then link to the full example.

[hamishwillee]

This looks pretty cool except that after pressing any of these buttons the bar fades and I can't get it back. I can still press the invisible buttons, but to make the bar reappear I need to refresh the page - not ideal

Edit - this is using latest chrome on refresh, which is still 149

[chrisdavidmills]

@hamishwillee darnit, adding the usage of the interrupted property from the fulfillment value completely broke it in non-supporting browsers ;-)

To fix this up, I've added a feature detection function and used that to register different event handlers depending on whether the browser supports the promise-returning scroll functions.

I'm then intending to just add a note about the feature detection in the articles, but I thought I'd ask your opinion first.

I'd rather do it this way to avoid making the event handler explanation any more complicated in the articles.

[hamishwillee]

I think that makes sense.

[pepelsbey]

Looks good! Thank you 🙂

Just a few suggestions for readmes and titles.

[chrisdavidmills]

Looks good! Thank you 🙂

Just a few suggestions for readmes and titles.

Super, ta!