JavaScript Sets are Excellent!

Jacob Evans on July 17, 2019

Sets In JavaScript Are 🔥 In MDN Set it states "The Set object lets you store unique values of any type, whether primitive values or obj... [Read Full]
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Cool read!

Fun 'interview style' question that can utilize sets:
Return an array of unique characters from the string 'Hello World', excluding spaces:

*** MY ANSWER ***

new Set('hello world'.split(' ').reduce((acc, cur) => acc.concat([...cur]), []));

  • OR using new flatMap operator -

new Set('hello world'.split(' ').flatMap(cur => [...cur]));


Cool I guess you could also do
[ Set([...'Hello World'])]


Almost, it won't exclude the space so you'd have to do something like [ Set([...'Hello World'.replace(/\s/g, '')])] which kinda ruins how nice and concise this was :(


I've been pretty impressed by the potential of sets before. I feel a little confused


I'd seen them used before to make iterable objects of some kind. I didn't fully understand it. But here you're using it to remove duplicates from an array. Is this the intended behavior of sets?

It is not the only intended use for Sets, they are also wicked fast and efficient at locating elements to see if they exist and deleting elements. Both are built-in functionality for Sets. I like to think of sets as almost a Hybrid of Maps and Arrays, its a bit of an oversimplification and generalization but I personally like thinking about them in that way.

One major difference is Arrays are Indexed collections while Sets are Keyed collections, which allows for some of the behaviors I mentioned that are similar to Maps like .has and .delete() and also related to why duplicates are not allowed (Maps also can't have duplicates)

I didn't know that map was its own type of object - in addition to a function on an array

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