My ideal would be a thing that says "this hit 90% of deployed browsers 4 years ago", but just seeing the date it was added to each of the significant browser families would be amazingly useful.
Using the Web Locks API page as an example, let's say we want to know when `LockManager` was added to Chrome. Here are the steps:
1. View the page: https://developer.mozilla.org/en-US/docs/Web/API/Web_Locks_A... 2. Scroll down to the Browser compatibility table 3. Find the cell you're interested in, in this example we're looking at where the `LockManager` row meets the Chrome column. 4. We see a check and a version number (in this case 69).
So at this point we know that it has existed since version 69.
Now in the case that we don't know that Chrome's current version is already < 100 and we need to know when a feature gained support:
5. Click on the cell to view the timeline of that cell.
Now we know that it was released on 2018-09-04, and it never had a smaller release requiring browser flags/prefixes/experiment flags/etc...
Now I'm digging around in https://github.com/mdn/browser-compat-data/blob/main/api/Loc... and trying to find the browser release dates data...
Ooh, https://bcd.developer.mozilla.org/bcd/api/v0/current/api.Loc... is even better - it expands those browser dates and it's served with access-control-allow-origin: *
It lets you search for an API and then displays a timeline. Details on how I built it here: https://github.com/simonw/tools/commit/59323c6a30271c856aabb... and https://github.com/simonw/tools/commit/472b46fda02e912c43604...