Function length

test/dummyStorageDriver.js:185–198

(callback)

    }

    function length(callback) {
        var self = this;
        var promise = new Promise(function(resolve, reject) {
            self
                .keys()
                .then(function(keys) {
                    resolve(keys.length);
                })
                .catch(reject);
        });

        executeCallback(promise, callback);
        return promise;
    }

    function removeItem(key, callback) {
        var self = this;