IDBCursor: continuePrimaryKey()

continuePrimaryKey(key, primaryKey)

let request = articleStore.index("tag").openCursor();
let count = 0;
let unreadList = [];
request.onsuccess = (event) => {
  let cursor = event.target.result;
  if (!cursor) {
    return;
  }
  let lastPrimaryKey = getLastIteratedArticleId();
  if (lastPrimaryKey > cursor.primaryKey) {
    cursor.continuePrimaryKey("javascript", lastPrimaryKey);
    return;
  }
  // lastIteratedArticleId 
  setLastIteratedArticleId(cursor.primaryKey);
  // unreadList  5 
  unreadList.push(cursor.value);
  if (++count < 5) {
    cursor.continue();
  }
};