What is Set

Set objects are collection of values.

• Values in Sets are unique
• can only occur once in a Set collection.

Set has different methods than Array and Map.

// Create a Set
const someSet = new Set(["a","b"]);

// adding element
someSet.add("c");
console.log(someSet); // ["a","b","c"]

// adding existing element, rejected
someSet.add("c");
console.log(someSet); // ["a","b","c"]

// checking item existence
someSet.has("a"); // true
someSet.has("d"); // false

Caveat

Objects added to Set are not unique by value.

const nSet = new Set();
nSet.add({name:'a', value: 'b'});
nSet.add({name:'a', value: 'b'});

console.log(nSet); // {Object {name: "a", value: "b"}, Object {name: "a", value: "b"}}

You need to stringify them to keep uniqueness.

nSet.add(JSON.stringify({name:'a', value: 'b'}))
nSet.add(JSON.stringify({name:'a', value: 'b'}))

const formattedSet = [...nSet].map(item) => {
  if (typeof item === 'string') return JSON.parse(item);
  else if (typeof item === 'object') return item;
});