Vue 3.6 Beta: The Vapor Mode Revolution and the New Reactivity Engine

The Vue ecosystem has reached a turning point with the release of version 3.6.0-beta.1. This update is not an incremental step; it's a deep re-engineering that prepares Vue for a future where the Virtual DOM (VDOM) is no longer the absolute protagonist.

In this article, we break down the two pillars of this beta: the arrival of "Feature Parity" in Vapor Mode and the new signals engine inspired by alien-signals.

Vapor Mode: Achieving "Feature Parity"

Until recently, Vapor Mode was a promising but limited experiment. With version 3.6, the core team announces that Feature Parity has been achieved.

What does "Feature Parity" mean exactly?

In software development, this term means that a new implementation (in this case, the Vapor compiler) is now capable of doing exactly the same as the original implementation (the standard VDOM compiler).

For us developers, this means that Vapor is no longer just for "simple components". It now supports:

• Full control directives: Complex handling of v-if, v-for (with optimized node movement algorithms), and v-model.
• Component Architecture: Support for Scoped Slots, dynamic components (<component :is="...">), and KeepAlive.
• Built-in features: Native support for <Teleport> and the <Transition> system.

In summary: Feature parity allows a complex production component to be compiled in Vapor mode without losing any Vue feature, while gaining unprecedented execution speed.

Refactoring @vue/reactivity: The "Alien" Effect

The big technical surprise in Vue 3.6 is the integration of alien-signals concepts (an ultra-fast signals library created by Johnson Chu, a core team member) into Vue's core.

Why change the signals' engine?

Vue 3's reactivity system based on Proxy was excellent, but it suffered in two areas: memory usage and dependency cleanup. The adoption of the alien-signals model solves this by changing the internal data structure.

The technical change: From Set to Linked Lists

Traditionally, Vue stored "subscribers" (the effects that must execute when data changes) in Set objects.

• The Problem: Creating thousands of Set objects consumes a lot of memory and stresses the Garbage Collector.
• The Solution: The new engine uses a Doubly Linked List. Subscriptions connect to each other like links in a chain.

The real benefits are impressive:

1. Memory Reduction: Up to 14% - 20% less consumption in applications with high state density.
2. O(1) Operations: Adding or removing a reactive subscription now has a constant cost, regardless of how many dependencies exist.
3. Smart Computed: The cleanup algorithm has been refined, preventing computed properties from being unnecessarily recalculated when dependencies haven't actually changed.

Comparison: VNode vs. Vapor Mode

To understand why this is a revolution, let's compare what happens "under the hood" with a basic component.

Source Code

<script setup>
import { ref } from 'vue'
const count = ref(0)
</script>
 
<template>
  <button @click="count++">Counter: {{ count }}</button>
</template>

// Vapor Mode is exclusive to the Composition API. There is no support available for the Options API.

The traditional approach (Virtual DOM)

Vue creates a JavaScript object (VNode) that represents the button. When count changes, Vue creates a new VNode, compares both (diffing), and decides which part of the real DOM to update. This happens in milliseconds, but has a CPU and memory cost.

The Vapor approach (Straight to the point)

The Vapor compiler generates code that "points" directly to the button's text node.

import { delegateEvents, t, setInterpolation, renderEffect } from '@vue/runtime-vapor'
 
const t0 = t('<button></button>') // Static template
 
export function render(_ctx) {
  const el0 = t0() 
  delegateEvents(el0, 'click', () => _ctx.count++)
  
  // No tree comparison. There's a direct "link".
  renderEffect(() => {
    setInterpolation(el0, () => `Counter: ${_ctx.count}`)
  })
  
  return el0
}

Result: Zero Virtual DOM, zero comparison algorithms, only direct DOM manipulation with maximum efficiency.

Performance and Capabilities Table

How to Get Started?

To experiment with these improvements, you need to use the beta version and configure your Vite environment to recognize Vapor mode.

Step 1: Installation

npm install vue@3.6.0-beta.1

pnpm add vue@3.6.0-beta.1

yarn add vue@3.6.0-beta.1

bun add vue@3.6.0-beta.1

Step 2: Vite Configuration

Enable support for .vapor.vue files (the recommended convention for differentiating components):

import { defineConfig } from 'vite'
import vue from '@vitejs/plugin-vue'
 
export default defineConfig({
  plugins: [
    vue({
      vapor: true // Enable the Vapor compiler
    })
  ]
})

Step 3: Using Components

You can mix standard and Vapor components. To force a component to use the new engine, use the .vapor.vue extension or define the script block:

<script setup vapor>
// This component will compile without Virtual DOM
</script>

Conclusion

Vue 3.6 is not just an update; it's a clear message to the community: Vue can be as fast and lightweight as any other framework, without sacrificing its beloved syntax. By integrating the efficiency of alien-signals and achieving functional parity with Vapor, Vue positions itself as the most flexible and powerful framework for the next decade of web development.