JSFiddle - React, Tailwind, and code Playground

JavaScript

var set = new Set();

console.log(set.size); //Logs 5
console.log(set.has("a")); //Logs true
console.log(set.delete("a")); //Logs true, was deleted
console.log(set.has("a")); //Logs false
console.log(set.delete("a")); //Logs false, wasn't deleted, wasn't there.

set.forEach(function (value, key, setObj) {
    console.log(value, key, key === value, set === setObj);
});

set.clear();

console.log(set.size); //Logs 0

set.add("a")
   .add("b")
   .add("c");

console.log(set.has("a")); //Logs true
console.log(set.size); //Logs 3