MobX Quick Start Guide

Granular reads and writes

The object API is focused on giving you granular control over the observable properties of top-level data structures: objects, arrays, and maps. In doing so, they continue to play well with the MobX reactive system and ensure the granular changes you make are picked up by the reactions. The following APIs apply to observable objects/arrays/maps:

• get(thing, key): Retrieves the value under the key. This key can even be non-existent. When used in a reaction, it will trigger a re-execution when that key becomes available.
• set(thing, key, value) or set(thing, { key: value }): sets a value for the key. The second form is better for setting multiple key-value pairs at once. Conceptually, it is very similar to Object.assign() ...