Vue 3 Reactive Track/Trigger & Fast Diff (Longest Increasing Subsequence) Stepper

Interactive Rust Wasm sandbox stepping through Vue 3's 5-stage patchKeyedChildren Fast Diff algorithm, Longest Increasing Subsequence (LIS) anchors, and ReactiveEffect dependency tracking.

📖 Companion Source-Code Deep-Dive:
Vue 3 Architecture (Part 3): Runtime Renderer & App Creation → Vue 3 Architecture (Part 4): Component Instance Setup & Initialization →

⚡ 1. Vue 3 Fast Diff (patchKeyedChildren & LIS) Step-by-Step Animator

Powered by Rust Wasm `vue3_get_sequence`: inspect pointers (i, e1, e2), LIS stationary anchors, and minimal DOM moves.

DOM Moves: 0Mounts: 0Unmounts: 0
0. Initi = 0 · e1 = 0 · e2 = 0
💡 Initializing Rust Wasm Fast Diff Engine...
Old Children (c1)
#0Aie1
#1B
#2C
#3D
#4E
#5F
#6G
New Children (c2) & LIS Stationary Anchors
#0Aie2
#1B
#2E
#3C
#4D
#5H
#6F
#7G
🖥️ Real Browser DOM Order at Current Step
DOM[0]<li key="A">
DOM[1]<li key="B">
DOM[2]<li key="C">
DOM[3]<li key="D">
DOM[4]<li key="E">
DOM[5]<li key="F">
DOM[6]<li key="G">

🔗 2. Vue 3 Reactive Dependency Graph (targetMap -> depsMap -> Dep Set)

Click to mutate any reactive key below and watch how Vue 3 triggers only its subscribed ReactiveEffect set.

msg: "Hello Yunsin"RefImpl<string>
🎯 Component Render Effect (setupRenderEffect)
🎯 ComputedRefImpl (fullGreeting)
🎯 Watcher Pre-Flush Effect (watch(msg))
count: 1RefImpl<number>
🎯 Component Render Effect (setupRenderEffect)
theme: "dark"ReactiveProxy.theme
🎯 Component Render Effect (setupRenderEffect)
1. Component Render Effect (setupRenderEffect)Runs: 1

Subscribed to [msg, count, theme]. Schedules component re-render in microtask queue (`queueJob`).

2. ComputedRefImpl (`greeting = computed(() => msg.value)`)Evaluations: 1

Subscribed ONLY to [msg]. Modifying `count` or `theme` leaves this Computed dirty=false.

3. Watcher Callback (`watch(() => msg.value, cb)`)Triggered: 0

Subscribed ONLY to [msg]. Fires callback when `msg` changes.
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Understanding Vue 3 Runtime: Fast Diff & Reactive Dependency Tracking

Use the interactive stepper above to inspect how Vue 3 synchronizes head and tail VNodes (`i`, `e1`, `e2`) and computes the Longest Increasing Subsequence (`getSequence`) to minimize DOM mutations.

Frequently Asked Questions (FAQ)

Q1 Why does Vue 3 compute the Longest Increasing Subsequence (LIS) during DOM diffing?
Moving real DOM nodes is much more expensive than JavaScript array operations. By finding the Longest Increasing Subsequence of old indices within the new child order in O(n log n) time, Vue 3 keeps the maximum possible number of DOM elements stationary and only moves the remaining nodes.