const id = Symbol("id");          // "id" is just a description (label)
const user = { [id]: 123, name: "Asha" };
user[id];                          // 123

const id2 = Symbol("id");
id === id2;                        // false — every symbol is unique

git add file.txt       # stage one file
git add src/           # stage a folder
git add .              # stage everything changed
git add -p             # stage interactively, hunk by hunk

const animal = {
  eat() { return "eating"; },
};

const dog = Object.create(animal);   // dog's prototype is animal
dog.bark = () => "woof";

dog.bark();   // "woof"    (own property)
dog.eat();    // "eating"  (found on the prototype)

function hasCycle(head) {
  let slow = head;
  let fast = head;

  while (fast !== null && fast.next !== null) {
    slow = slow.next;
    fast = fast.next.next;
    if (slow === fast) return true;
  }

  return false;
}