---
title: "Level 3: Reactivity and lifecycle · Bug Hunt · vuejs.school"
description: "Watchers that never fire, state that goes missing and a hook that crashes the mount."
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> Index of every page on this site: [llms.txt](https://vuejs.school/llms.txt)

**Level 3 of 3 · watch sources, state, hooks and computeds**

# **Reactivity and lifecycle**

Watchers that never fire, state that goes missing and a hook that crashes the mount.

**Round 1 of 5**

## **The watcher never runs**

One line is wrong. Click it in the component.

**Game finished**

## **You finished Bug Hunt**

All 3 levels done. Two more games are waiting for you.

- [  1. **1****App****setup**  2. **2****App****onBeforeMount**  3. **3****App****onMounted****Ordering puzzle****Lifecycle Line-up**Put the lifecycle hooks in the order Vue fires them.0 of 7 levels done**Start playing**](https://vuejs.school/games/lifecycle)
- [**Preview****1****re-rendered****+1****Prediction game****Reactivity Radar**Will the template update? Call it before Vue does.0 of 3 levels done**Start playing**](https://vuejs.school/games/radar)

[**All games**](https://vuejs.school/games) [**Play again from level 1**](https://vuejs.school/games/bug-hunt/1)

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