How to iterate over a list of keys using a cursor, using IndexedDB.

idb_key_list.js

// Copyright 2019 Google LLC.
// SPDX-License-Identifier: Apache-2.0

var name = 'db' + Date.now();
var openReq = indexedDB.open(name, 1);
openReq.onupgradeneeded = function() {
  var db = openReq.result;
  var store = db.createObjectStore('store');
  for (var i = 0; i < 100; i += 10)
    store.put("record-" + i, i);
};
openReq.onsuccess = function() {
  var db = openReq.result;
  var tx = db.transaction('store', 'readwrite');
  var store = tx.objectStore('store');

  var compare = indexedDB.cmp.bind(indexedDB);
  var keys = [ 25, 35, 45, 30, 40, 50, 50, 25 ];
  sort_unique(keys, compare);

  function emit(k, v) { console.log([k, v]); }

  var r = store.openCursor(IDBKeyRange.bound(keys[0], keys[keys.length-1]));
  r.onsuccess = function() {
    var cursor = r.result;
    if (cursor) {
      while(keys.length && indexedDB.cmp(keys[0], cursor.key) <= 0)
        keys.shift();
      emit(cursor.key, cursor.value);
      if (keys.length)
        cursor.continue(keys[0]);
    }
  };
};

function sort_unique(array, compare) {
  array.sort(compare);
  var i = 1;
  while (i < array.length) {
    if (compare(array[i], array[i-1]) === 0) {
      array.splice(i, 1);
    } else {
      ++i;
    }
  }
}