how to add to a document firestore code example

Example 1: firestore set a document

let data = {
  name: 'Los Angeles',
  state: 'CA',
  country: 'USA'
};

// Add a new document in collection "cities" with ID 'LA'
let setDoc = db.collection('cities').doc('LA').set(data);

Example 2: firebase cloud method update

firebase deploy --only functions:functionNameHere