This snippet shows how to user cursors with IndexedDB to loop through results

cursors-indexeddb.js

// Offline Web Applications course on Udacity https://classroom.udacity.com/courses/ud899

//Starting with "Group data together using indexes" snippet in https://gist.github.com/luke-denton/193fd42e9fcfe6e2f1e8b6c4de58dc4e

//Basically a complicated way of calling getAll()
dbPromise.then(function(db) {
  var tx = db.transaction('people');
  var peopleStore = tx.objectStore('people');
  var superheroIndex = peopleStore.index('superhero');
  
  return superheroIndex.openCursor();
}).then(function() { //Showing how to skip items in the loop
  return cursor.advance(2); //This will skip the first 2 items in the results, so they won't be changed/deleted etc, just returned as they are
}).then(function logPerson(cursor) {
  if (!cursor) return;
  
  //Potential Actions
  //cursor.update(newValue); //Change the value of the object that the cursor is pointing to
  //cursor.delete(); //Delete the item that the cursor is pointing to
  
  //cursor.continue() returns a Promise for a cursor representing the next item
  //Passing logPerson into the then() function means the cursor for the next item will be passed into
  //this function and processed
  return cursor.continue().then(logPerson);
}).then(function() {
  //Done cursoring
});