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

IDBObjectStore: deleteIndex() method - Web APIs

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Note: This feature is available in Web Workers.

The deleteIndex() method of the IDBObjectStore interface destroys the index with the specified name in the connected database, used during a version upgrade.

Note that this method must be called only from a VersionChange transaction mode callback. Note that this method synchronously modifies the IDBObjectStore.indexNames property.

indexName

The name of the existing index to remove.

None (undefined).

InvalidStateError DOMException

Thrown if the method was not called from a versionchange transaction mode callback.

TransactionInactiveError DOMException

Thrown if the transaction this IDBObjectStore belongs to is not active (e.g., has been deleted or removed.)

NotFoundError DOMException

Thrown if there is no index with the given name (case-sensitive) in the database.

In the following example you can see the onupgradeneeded handler being used to update the database structure if a database with a higher version number is loaded. IDBObjectStore.createIndex is used to create new indexes on the object store, after which we delete the unneeded old indexes with deleteIndex(). For a full working example, see our To-do Notifications app (view example live).

let db;

// Let us open our database
const DBOpenRequest = window.indexedDB.open("toDoList", 4);

// these two event handlers act on the database being opened successfully, or not
DBOpenRequest.onerror = (event) => {
  note.appendChild(document.createElement("li")).textContent =
    "Error loading database.";
};

DBOpenRequest.onsuccess = (event) => {
  note.appendChild(document.createElement("li")).textContent =
    "Database initialized.";

  // store the result of opening the database in the db variable. This is used a lot below
  db = event.target.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
DBOpenRequest.onupgradeneeded = (event) => {
  const db = event.target.result;

  db.onerror = (event) => {
    note.appendChild(document.createElement("li")).textContent =
      "Error loading database.";
  };

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

  // define what data items the objectStore will contain

  objectStore.createIndex("hours", "hours", { unique: false });
  objectStore.createIndex("minutes", "minutes", { unique: false });
  objectStore.createIndex("day", "day", { unique: false });
  objectStore.createIndex("month", "month", { unique: false });
  objectStore.createIndex("year", "year", { unique: false });
  objectStore.createIndex("notified", "notified", { unique: false });

  objectStore.deleteIndex("seconds");
  objectStore.deleteIndex("contact");
};

• 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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