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Showing content from http://developer.mozilla.org/en-US/docs/Web/API/IDBCursor/continuePrimaryKey below:

IDBCursor: continuePrimaryKey() method - Web APIs

Baseline Widely available

Note: This feature is available in Web Workers.

The continuePrimaryKey() method of the IDBCursor interface advances the cursor to the item whose key matches the key parameter as well as whose primary key matches the primary key parameter.

A typical use case, is to resume the iteration where a previous cursor has been closed, without having to compare the keys one by one.

Calling this method more than once before new cursor data has been loaded - for example, calling continuePrimaryKey() twice from the same onsuccess handler - results in an InvalidStateError being thrown on the second call because the cursor's got value flag has been unset.

This method is only valid for cursors coming from an index. Using it for cursors coming from an object store will throw an error.

continuePrimaryKey(key, primaryKey)

key

The key to position the cursor at.

primaryKey

The primary key to position the cursor at.

None (undefined).

This method may raise a DOMException of one of the following types:

TransactionInactiveError DOMException

Thrown if this IDBCursor's transaction is inactive.

DataError DOMException

Thrown if the key parameter has any of the following conditions:

• The key is not a valid key.
• The key is less than or equal to this cursor's position and the cursor's direction is next or nextunique.
• The key is greater than or equal to this cursor's position and this cursor's direction is prev or prevunique.

InvalidStateError DOMException

Thrown if the cursor is currently being iterated or has iterated past its end.

InvalidAccessError DOMException

Thrown if the cursor's direction is not prev or next.

here's how you can resume an iteration of all articles tagged with "javascript" since your last visit:

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;
  }
  // update lastIteratedArticleId
  setLastIteratedArticleId(cursor.primaryKey);
  // preload 5 articles into the unread list;
  unreadList.push(cursor.value);
  if (++count < 5) {
    cursor.continue();
  }
};

• Using IndexedDB
• Starting transactions: IDBDatabase
• Using transactions: IDBTransaction
• Setting a range of keys: IDBKeyRange
• Retrieving and making changes to your data: IDBObjectStore
• Using cursors: IDBCursor
• Reference example: To-do Notifications (View the example live).

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