Sets

JavaScript added support for sets back in 2015 (still waiting on you to do the same, Golang...). A set is just a collection of unique values.

Sets are fantastic for de-duplication and checking if a value exists in a collection.

const set = new Set([1, 2, 3, 4, 5, 5, 5, 5]);
console.log(set);
// Set { 1, 2, 3, 4, 5 }

Notice that all duplicate instances of 5 were collapsed into one in the set. You can also add and delete values dynamically:

const set = new Set();
set.add("bertholdt");
set.add("reiner");
set.add("annie");
set.add("bertholdt");
console.log(set);
// Set { 'bertholdt', 'reiner', 'annie' }

set.delete("annie");
console.log(set);
// Set { 'bertholdt', 'reiner' }