Spread operator applied to object literals and not just arrays const obj1 = { "firstName": "James", "lastName": "Holden" } const obj2 = { ...obj1, "rank": "captain" } const addRank = true; console.log(obj2); // { firstName: "James", lastName: "Holden", rank: "captain&

const asyncTask = () => new Promise((_resolve, reject) => setTimeout(() => reject("Something not working!"), 1e3) ); const foo = () => asyncTask() .then(console.log) // Logs Promise .catch(console.error) // Logs the failure .finally(() => console.log("After calling AsyncTask")); // Logs the completion foo(); Source

Array explorer Object explorer

Shallow compare using Array​.prototype​.every()

Spread and Set operators