Creating a Set
A Set stores unique values of any type.
const set = new Set();
set.add(1);
set.add(2);
set.add(2); // duplicate, ignored
set.add("hello");
console.log(set.size); // 3has and delete
Check values with has, remove with delete, clear all with clear.
const tags = new Set(["js", "html", "css"]);
console.log(tags.has("js")); // true
console.log(tags.has("php")); // false
tags.delete("css");
console.log(tags.size); // 2
tags.clear();
console.log(tags.size); // 0Removing Duplicates from Arrays
Pass an array to the Set constructor to get unique values.
const numbers = [1, 2, 2, 3, 3, 3, 4, 5, 5];
const unique = [...new Set(numbers)];
console.log(unique); // [1, 2, 3, 4, 5]
const word = "hello";
const letters = new Set(word);
console.log([...letters].join("")); // "helo"Iterating a Set
Sets are iterable and maintain insertion order.
const fruits = new Set(["apple", "banana", "cherry"]);
fruits.forEach(fruit => console.log(fruit));
for (const fruit of fruits) {
console.log("I like " + fruit);
}Set Operations (Manual)
JavaScript does not have built-in set operations, but they are easy to implement.
const setA = new Set([1, 2, 3, 4]);
const setB = new Set([3, 4, 5, 6]);
const union = new Set([...setA, ...setB]);
console.log([...union]); // [1, 2, 3, 4, 5, 6]
const intersection = new Set([...setA].filter(x => setB.has(x)));
console.log([...intersection]); // [3, 4]
const difference = new Set([...setA].filter(x => !setB.has(x)));
console.log([...difference]); // [1, 2]