In terms of real world usage, unless you have multiple thousands of objects in your array it is not going to matter which approach you use. This method is for developer convenience.

You can group by length of keys yes. There is no sorting in an object. The order in an object is based on the order that the keys were added.

You can post tutorial requests here - kzfaq.info/get/bejne/gqmVrcSpl9uyY5c.html

It really depends on what you are trying to do. You might want to use reduce or flatMap

It doesn't return an array, so closer to the reduce method

It returns an Object not an array. The Map object also has a groupBy method if the keys are not strings or symbols.

@@SteveGriffith-Prof3ssorSt3v3 so does reduce, this clearly a collection processing functionality, this belongs in array, this bad design.

If all you are doing is what you did in that reduce statement, then with the new groupBy you could reduce all the code into this one line: Object.groupBy(movies, ({series})=>series); which I would argue is much easier to read and understand than the reduce method. I've been teaching Array.reduce to students for years and they frequently struggle with the syntax. The more complex the situation, the more options that you are adding, the longer the code becomes, regardless of which option you pick.

You don't see the benefit of writing less code vs. more code? Wow. Where do you work, so we can all know not to apply?

????????!!! This exists in almost every main language out there. It’s not over engineering. It’s a common task that shouldn’t need so much boilerplate to achieve.