IDBOpenDBRequest.onblocked - Web APIs 编辑

The onblockedevent handler of the IDBOpenDBRequest interface is the event handler for the blocked event. This event is triggered when the upgradeneeded should be triggered because of a version change but the database is still in use (that is, not closed) somewhere, even after the versionchange event was sent.

Note:

Syntax

IDBOpenDBRequest.onblocked = function(event) { ... };

Example

var db;

// Let us open our database
var request = indexedDB.open("toDoList", 4);

// these two event handlers act on the database being opened
// successfully, or not
request.onerror = function(event) {
  note.innerHTML += '<li>Error loading database.</li>';
};

request.onsuccess = function(event) {
  note.innerHTML += '<li>Database initialised.</li>';

  // store the result of opening the database in the db variable.
  // This is used a lot below
  db = request.result;

  // Run the displayData() function to populate the task list with
  // all the to-do list data already in the IDB
  displayData();
};

// This event handles the event whereby a new version of the
// database needs to be created. Either one has not been created
// before, or a new version number has been submitted via the
// window.indexedDB.open line above
//it is only implemented in recent browsers
request.onupgradeneeded = function(event) {
  var db = event.target.result;

  db.onerror = function(event) {
    note.innerHTML += '<li>Error loading database.</li>';
  };

  // Create an objectStore for this database
  var objectStore = db.createObjectStore("toDoList", { keyPath: "taskTitle" });

  ...
};

request.onblocked = function() {
  console.log("Your database version can't be upgraded because the app is open somewhere else.");
}

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• 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 example live.)
• blocked event