Common ES6 Mistakes

const myObject = {
  emails: null
}

const { emails = [], users = [] } = myObject;

console.log(users.length);   // users is undefined (defaults to []) This returns 0.
console.log(emails.length);  // this will bork; you can't get length of null.

Strings are iterables

const set = new Set('555')
console.log(set);   // {'5'}

More to come as I continue to make more mistakes…