Discussion on: 60fps with Functional Programming in idle time

Ok that keyBy might be an issue if the data is huge. You/I/we could do a version of keyBy that uses reduceAsync and that would split it up over frames. Fundamentally that would probably look like this:

function keyByAsync(items, predicate) {

    return reduceAsync(items, reducer, {})
    function reducer(acc, cur) {
        acc[predicate(cur)] = cur
        return acc
    }
}

      await keyByAsync(yourArray, v=>v.somethingOrOther)

That's making a single lookup rather than a key to array - but it sounds like this is what you are after. It's a useful function, I may clean it and a few others like groupBy and add them. Basically anything that takes a while benefits from going through one of the async functions which yield every 8 times (by default) to see if there is still time.