# Reactivity and signals: demystifying frontend magic

> Unpack frontend reactivity: change propagation, dependency tracking, signals, computed values, and effects in modern frameworks.

- Date: 2025-12-05
- Event: [DevFest Dijon](<https://devfest.developers-group-dijon.fr/>)
- Location: Dijon, France
- Topics: computed-values, dependency-tracking, effects, frontend-reactivity, signals, vue

## Resources

- [Slides](<https://talks.soubiran.dev/2025-12-05/devfest-dijon>)
- [PDF](<https://talks.soubiran.dev/2025-12-05/devfest-dijon/pdf>)
- [Source code](<https://talks.soubiran.dev/2025-12-05/devfest-dijon/src>)

## Summary

Reactive rendering depends on knowing which computations use which pieces of state. This talk explores that relationship with `alien-signals`, from the basic `signal`, `computed`, and `effect` APIs to the data structures used to track dependencies.

It explains how updates propagate, why reactive systems need to deal with cycles and mutable state, and how a small signal-based framework can update the DOM. The final example connects the same ideas to Vue's `ReactiveEffect`.