proposal-cancellation VS proposal-array-find-from-last

To cancel a task, you'll have to do that plumbing yourself, and it depends on what you're wanting to cancel. Most libraries provide some sort of mechanism to do the cancelation. The fetch API allows you to pass in an abort controller, which provides a way for you to signal to the running fetch request to abort. setTimeout() has clearTimeout(). In Node, if you read a file as a stream instead of a simple fs.promises.readFile(), you'll have the power to just stop trying to grab more data from the stream. Each async API has its own way to enable aborting (or, sometimes it doesn't provide any way to abort at all). There's unfortunately no standard way to handle aborting (though there is this stalled JavaScript proposal that attempted to standardize an abort system).

Finally, one other related and important concept is the token-based cancelation of asynchronous subscriptions (the current TC39 proposal), which I plan to cover later. If you find these topics interesting, consider following me on Twitter for any updates.

Array find from last

Apparently there is a proposal for .findLast() and .findLastIndex().

Proposal page: proposal-array-find-from-last.

Array find from last: findLast() and findLastIndex() methods on Array.prototype.