the.com/reactivity
Change one cell, and a spreadsheet of code quietly rebuilds itself around you.
means A property of a system where changes to underlying data automatically and efficiently propagate to everything that depends on it.
from From 'reactive,' built on Latin re- ('back, again') plus agere ('to do, to drive, to act') — the same root that gives us 'act' and 'agent.' Something reactive acts back, responding to a push rather than waiting to be asked. The word existed in general use for centuries (chemistry borrowed it early, for substances quick to respond to other substances), but computing seized it in the late 20th century for systems designed to respond automatically to change — spreadsheets being the original, humble proof that the idea worked, long before it had a name.
- origin
- spreadsheets had this in 1979, code caught up decades later
- mechanism
- tracks dependencies, reruns only what actually changed
- tradeoff
- magic convenience hides real cost: debugging invisible update chains
- modern form
- signals replaced dirty-checking because polling everything is lazy