Ability to get many items (aka. getItems())

After doing some performance measurements on my app I notice I suffer a lot from doing this:

localForage.getItem('all_ids', function(ids) {
    _.each(ids, function(id) {
        localForage.get(id, function(value) {
            ...
        });
    })
})

This is causing a lot of excess work for the browser if the list is long (e.g. 1,000+).

I know the localStorage spec doesn’t have support getItems() but in most cases IndexDB is supported and it appears to have low level support for getting multiple keys which could hopefully reduce the overhead in total.

For the localStorage fallback, this would be trivial to wrap up with a for loop of kinds.

[tofumatt]

@thgreasi wrote in #291 an API I like for these multi-item calls:

How about:

Promise.all([
    localforage.getItem('item1'),
    localforage.getItem('item2')
]).then(function(results) {
    console.log(results);
});

// OR

var items = ['item1', 'item2', 'item3'];
var promises  = items.map(function(item) { return localforage.getItem(item); });
Promise.all(promises).then(function(results) {
    console.log(results);
});

If getItems() / setItems() are going to be implemented by localforage at some point, then something like the 2nd example might actually have to be used by some drivers.

[tamer1an]

Yes, it would be convenient. Please consider adding that feature. :godmode: