Consider adding some way to retrieve secondary keys when using IDBIndex.getAllKeys

[malibuzios]

When using IDBIndex.openKeyCursor to retrieve all (index) keys satisfying some range, I can easily get the secondary key (the value of the property indexed for that particular record) in addition to the primary one, for example:

...
let results = [];

let cursorRequest = objectStore.index("myIndex").openKeyCursor(range);

cursorRequest.onsuccess = (event) => {
    let cursor = event.target.result;

    if (cursor) {
        results.push({ primaryKey: cursor.primaryKey, key: cursor.key });
        cursor.continue();
    }
    else {
        resolve(results);
    }
}
...

It seems that IDBIndex.getAllKeys currently only returns the primary keys (tested on latest stable Firefox/Chrome versions). Is/will there be any way to retrieve the secondary keys as well? or falling back to using cursors is planned to remain the most efficient solution?

[tophf]

In my tests IDBIndex.openKeyCursor on 4000 of relatively simple records seems to be practically unusable in Chrome - 150ms compared to 15ms of IDBIndex.getAllKeys.

[inexorabletash]

#206 is a dupe of this, but has more context.