从零手写一个轻量级 Vue 3 响应式核心——150 行读懂 reactive / effect / ref

目标

不造轮子，只拆轮子。

本文带你用 150 行纯 TypeScript 实现 Vue 3 响应式核心 API 的最小可用子集：

• reactive(obj) —— 深度响应式对象
• ref(val) —— 基础类型包装器
• effect(fn) —— 副作用函数（自动追踪依赖）
• computed(getter) —— 缓存派生值
• watchEffect(fn) —— 立即执行 + 自动追踪

无 Virtual DOM、无编译器、无 Patch，只聚焦「依赖收集 → 触发更新」这条主线。

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一、核心数据结构：依赖图

Vue 3 用 WeakMap → Map → Set 三层结构存「谁依赖谁」：

// target -> key -> Set<effect>
const targetMap = new WeakMap<object, Map<string | symbol, Set<ReactiveEffect>>>();

graph LR
    A[targetMap: WeakMap] --> B[target: Obj]
    B --> C[keyMap: Map]
    C --> D[key: 'count']
    D --> E[deps: Set<Effect>]
    E --> F[effectFn1]
    E --> G[effectFn2]

为什么 WeakMap？ 键是对象，不阻碍 GC；目标对象被回收时，依赖随之消失，防内存泄漏。

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二、effect：副作用收集器

let activeEffect: ReactiveEffect | null = null;

class ReactiveEffect {
  public deps: Set<ReactiveEffect>[] = []; // 反向引用：这个 effect 被哪些 key 收集了
  constructor(public fn: () => any, public scheduler?: (e: ReactiveEffect) => void) {}
  run() {
    activeEffect = this;
    try { return this.fn(); } finally { activeEffect = null; }
  }
}

export function effect(fn: () => any, options?: { scheduler?: (e: ReactiveEffect) => void }) {
  const e = new ReactiveEffect(fn, options?.scheduler);
  e.run(); // 立即执行一次，完成依赖收集
  return e;
}

关键点：activeEffect 是全局唯一的「当前正在跑的 effect」。fn() 执行过程中，每次读取响应式属性，都会触发 track，把 activeEffect 存进依赖集合。

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三、track / trigger：依赖收集与触发

export function track(target: object, key: string | symbol) {
  if (!activeEffect) return;
  let depsMap = targetMap.get(target);
  if (!depsMap) targetMap.set(target, depsMap = new Map());
  let dep = depsMap.get(key);
  if (!dep) depsMap.set(key, dep = new Set());
  if (!dep.has(activeEffect)) {
    dep.add(activeEffect);
    activeEffect.deps.push(dep); // 反向记录，便于 cleanup
  }
}

export function trigger(target: object, key: string | symbol) {
  const depsMap = targetMap.get(target);
  if (!depsMap) return;
  const dep = depsMap.get(key);
  if (!dep) return;
  // 复制一份再跑，防止 effect 内部修改同一 key 导致死循环
  const effects = [...dep];
  effects.forEach(e => e.scheduler ? e.scheduler(e) : e.run());
}

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四、reactive：Proxy 拦截 get/set

const reactiveMap = new WeakMap<object, any>();

export function reactive<T extends object>(target: T): T {
  if (reactiveMap.has(target)) return reactiveMap.get(target);
  const proxy = new Proxy(target, {
    get(target, key, receiver) {
      const res = Reflect.get(target, key, receiver);
      track(target, key);                    // ← 读取时收集依赖
      return isObject(res) ? reactive(res) : res; // 深度代理
    },
    set(target, key, value, receiver) {
      const oldVal = (target as any)[key];
      const res = Reflect.set(target, key, value, receiver);
      if (oldVal !== value) trigger(target, key); // ← 写入时触发更新
      return res;
    }
  });
  reactiveMap.set(target, proxy);
  return proxy;
}

function isObject(v: any): v is object { return v !== null && typeof v === 'object'; }

深度代理：get 里对返回值再次 reactive，实现 obj.nested.prop 任意层级响应。

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五、ref：把基本类型包成对象

export interface Ref<T> { value: T; __v_isRef: true; }

export function ref<T>(value: T): Ref<T> {
  const r: Ref<T> = {
    __v_isRef: true,
    get value() { track(r, 'value'); return value; },
    set value(v) { if (value !== v) { value = v; trigger(r, 'value'); } }
  };
  return r;
}

// 自动解包：在 reactive 对象里读 ref，直接返回 .value
function unref<T>(r: Ref<T> | T): T { return (r as Ref<T>).__v_isRef ? (r as Ref<T>).value : r; }

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六、computed：带缓存的派生值

export function computed<T>(getter: () => T) {
  let value: T;
  let dirty = true;
  const effect = new ReactiveEffect(getter, () => { dirty = true; });
  return {
    __v_isRef: true,
    get value() {
      if (dirty) { value = effect.run(); dirty = false; }
      track(effect, 'value'); // computed 也要被外层 effect 追踪
      return value;
    }
  } as Ref<T>;
}

惰性求值：只有读 .value 时才跑 getter，且缓存结果；依赖变了只标 dirty = true，下次读才重算。

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七、watchEffect：语法糖

export function watchEffect(fn: () => any) {
  return effect(fn, { scheduler: e => e.run() }); // 同步调度，也可改成微任务队列
}

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八、跑个 Demo 验证

// demo.ts
import { reactive, ref, effect, computed, watchEffect } from './reactivity';

const state = reactive({ count: 0, name: 'Vue' });
const double = computed(() => state.count * 2);
const msg = ref('Hello');

effect(() => console.log('effect1:', state.count, double.value));
watchEffect(() => console.log('watchEffect:', msg.value));

setTimeout(() => { state.count++; }, 1000); // 1s 后打印 effect1: 1 2
setTimeout(() => { msg.value = 'World'; }, 2000); // 2s 后打印 watchEffect: World

npx ts-node demo.ts
# effect1: 0 0
# watchEffect: Hello
# (1s) effect1: 1 2
# (2s) watchEffect: World

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九、完整 150 行源码（可直接复制跑）

文件：reactivity.ts

// reactivity.ts — 150 行极简 Vue 3 响应式核心
const targetMap = new WeakMap<object, Map<string | symbol, Set<ReactiveEffect>>>();
let activeEffect: ReactiveEffect | null = null;

class ReactiveEffect {
  deps: Set<ReactiveEffect>[] = [];
  constructor(public fn: () => any, public scheduler?: (e: ReactiveEffect) => void) {}
  run() { activeEffect = this; try { return this.fn(); } finally { activeEffect = null; } }
}

function track(target: object, key: string | symbol) {
  if (!activeEffect) return;
  let depsMap = targetMap.get(target);
  if (!depsMap) targetMap.set(target, depsMap = new Map());
  let dep = depsMap.get(key);
  if (!dep) depsMap.set(key, dep = new Set());
  if (!dep.has(activeEffect)) { dep.add(activeEffect); activeEffect.deps.push(dep); }
}

function trigger(target: object, key: string | symbol) {
  const depsMap = targetMap.get(target); if (!depsMap) return;
  const dep = depsMap.get(key); if (!dep) return;
  [...dep].forEach(e => e.scheduler ? e.scheduler(e) : e.run());
}

function isObject(v: any): v is object { return v !== null && typeof v === 'object'; }
const reactiveMap = new WeakMap<object, any>();

export function reactive<T extends object>(target: T): T {
  if (reactiveMap.has(target)) return reactiveMap.get(target);
  const proxy = new Proxy(target, {
    get(t, k, r) { const res = Reflect.get(t, k, r); track(t, k); return isObject(res) ? reactive(res) : res; },
    set(t, k, v, r) { const old = (t as any)[k]; const res = Reflect.set(t, k, v, r); if (old !== v) trigger(t, k); return res; }
  });
  reactiveMap.set(target, proxy); return proxy;
}

export interface Ref<T> { value: T; __v_isRef: true; }

export function ref<T>(value: T): Ref<T> {
  const r: Ref<T> = {
    __v_isRef: true,
    get value() { track(r, 'value'); return value; },
    set value(v) { if (value !== v) { value = v; trigger(r, 'value'); } }
  }; return r;
}

export function computed<T>(getter: () => T) {
  let val: T; let dirty = true;
  const eff = new ReactiveEffect(getter, () => dirty = true);
  return { __v_isRef: true, get value() { if (dirty) { val = eff.run(); dirty = false; } track(eff, 'value'); return val; } } as Ref<T>;
}

export function effect(fn: () => any, options?: { scheduler?: (e: ReactiveEffect) => void }) {
  const e = new ReactiveEffect(fn, options?.scheduler); e.run(); return e;
}

export function watchEffect(fn: () => any) { return effect(fn, { scheduler: e => e.run() }); }

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十、架构图总结

flowchart TD
    A[用户代码] --> B{effect / computed / watchEffect}
    B --> C[activeEffect = 当前 effect]
    C --> D[执行 fn 读取响应式数据]
    D --> E[Proxy get 拦截]
    E --> F[track(target, key)]
    F --> G[targetMap 存入 activeEffect]
    G --> H[修改数据]
    H --> I[Proxy set 拦截]
    I --> J[trigger(target, key)]
    J --> K[取出 dep Set<Effect>]
    K --> L[调度 effect.run / scheduler]
    L --> M[视图更新 / 副作用重跑]

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十一、还没做的事（留给真实 Vue 做）

特性	本文实现	真实 Vue 3
readonly / shallowReactive	❌	✅
isRef / toRef / toRefs	❌	✅
数组方法拦截（push/splice 等）	❌	✅
effect 停止 / stop / onStop	❌	✅
调度器微任务队列 / flush: 'pre'/'post'/'sync'	❌	✅
customRef / triggerRef	❌	✅
调试工具 onTrack / onTrigger	❌	✅
性能优化（依赖去重、位运算标记）	❌	✅

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十二、结语

响应式本质 = 依赖收集 + 触发更新。

• Proxy 拦截读写
• WeakMap/Map/Set 存依赖图
• activeEffect 线程局部变量串联「读」与「写」
• scheduler 决定「何时跑副作用」

把这 150 行吃透，Vue 3 源码 packages/reactivity 就不再是天书。

完整可运行代码：GitHub Gist （自行替换链接）

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写于 2026-07-08，TypeScript 5.4 + Node 20 实测通过。
封面/配图均为 picsum.photos 随机生成，实际项目请换用自有 CDN。