IDBIndex: count() method
The count()
method of the IDBIndex
interface returns an IDBRequest
object, and in a separate thread,
returns the number of records within a key range.
Note: This feature is available in Web Workers
Syntax
js
count()
count(key)
Parameters
key
Optional-
The key or key range that identifies the record to be counted.
Return value
A IDBRequest
object on which subsequent events related to this operation are fired.
If the operation is successful, the value of the request's result
property is the number of records that match the given key or key range.
Exceptions
This method may raise a DOMException
of one of the following types:
TransactionInactiveError
DOMException
-
Thrown if this
IDBIndex
's transaction is inactive. DataError
DOMException
-
Thrown if the key or key range provided contains an invalid key.
InvalidStateError
DOMException
-
Thrown if the
IDBIndex
has been deleted or removed.
Examples
In the following example we open a transaction and an object store, then get the
index lName
from a simple contacts database. We then open a basic cursor on
the index using IDBIndex.openCursor
— this works the same as opening a
cursor directly on an ObjectStore
using
IDBObjectStore.openCursor
except that the returned records are sorted
based on the index, not the primary key.
myIndex.count()
is then used to count the number of records in the index,
and the result of that request is logged to the console when its success callback
returns.
Finally, we iterate through each record, and insert the data into an HTML table. For a complete working example, see our IndexedDB-examples demo repo (View the example live).
js
function displayDataByIndex() {
tableEntry.innerHTML = "";
const transaction = db.transaction(["contactsList"], "readonly");
const objectStore = transaction.objectStore("contactsList");
const myIndex = objectStore.index("lName");
const countRequest = myIndex.count();
countRequest.onsuccess = () => {
console.log(countRequest.result);
};
myIndex.openCursor().onsuccess = (event) => {
const cursor = event.target.result;
if (cursor) {
const tableRow = document.createElement("tr");
tableRow.innerHTML =
`<td>${cursor.value.id}</td>` +
`<td>${cursor.value.lName}</td>` +
`<td>${cursor.value.fName}</td>` +
`<td>${cursor.value.jTitle}</td>` +
`<td>${cursor.value.company}</td>` +
`<td>${cursor.value.eMail}</td>` +
`<td>${cursor.value.phone}</td>` +
`<td>${cursor.value.age}</td>`;
tableEntry.appendChild(tableRow);
cursor.continue();
} else {
console.log("Entries all displayed.");
}
};
}
Specifications
Specification |
---|
Indexed Database API 3.0 # ref-for-dom-idbindex-count① |
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 the example live).