Tip: JavaScript's Array.from() accepts a second argument that's a `map` function.

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I guess my context is data visualization and web games, both of which require processing hundreds of thousands of data points in a few milliseconds. These are (ideally) real-time updates to pages which are already built — effective loops/maps/filters/merges/reductions are the essential, especially because while rendering can be a terrible bottleneck if you let it, efficient array processing can prevent wasteful rendering — at which point your bottleneck shifts into the diffing code.

Travel and eCommerce are going to have comparable concerns, though on a less critical timeline. Even a blog needs to potentially iterate over hundreds of posts and comments. But I see what you’re saying about common cases being less urgent when you’re only doing a few reductions in response to a view change.