MobX is considered a Transparent functional reactive programming (TFRP) system. Yes, too many adjectives in that line! Let's break it down word by word.
Connecting the observables to the observers, it allows the observers to react to changes in observables. This is a basic expectation we have from MobX and the way we establish these connections feels very intuitive. There is no explicit wiring besides the use of decorators and dereferencing observables inside the observer. Because of the low overhead in wiring, MobX becomes very declarative, where you express your intent without worrying about the machinery. The automatic connections established between the observables and observers enables the reactive system to function autonomously. This makes MobX a transparent system as the work of connecting observables with observers is essentially lifted away. The usage of an observable inside a reaction is enough to wire the two.