if (config.onEntry) {
                        config.onEntry(entry);
                    }

Right now there is no entry!

                    if (config.onEntry) {
                        config.onEntry();
                    }

https://github.com/mintuz/horizon/blob/master/src/index.js#L43

As a result:
1 - docs are wrong

onEntry	(entry) => {}	Callback which is called when the element to observe is in view, triggers once if triggerOnce is set to true	N/A

2 - using this lib we can not get currently observed entry inside hooks!