refactor(reactivity): use more efficient reactive checks

WeakSets and WeakMaps shows degrading performance as the amount of
observed objects increases. Using hidden keys result in better
performance especially when repeatedly creating large amounts of
reactive proxies.

This also makes it possible to more efficiently declare non-reactive
objects in userland.

packages/reactivity/src/baseHandlers.ts

@@ -1,4 +1,4 @@
-import { reactive, readonly, toRaw } from './reactive'
+import { reactive, readonly, toRaw, ReactiveFlags } from './reactive'
 import { TrackOpTypes, TriggerOpTypes } from './operations'
 import { track, trigger, ITERATE_KEY } from './effect'
 import { isObject, hasOwn, isSymbol, hasChanged, isArray } from '@vue/shared'
@@ -35,6 +35,14 @@ const arrayInstrumentations: Record<string, Function> = {}
 
 function createGetter(isReadonly = false, shallow = false) {
   return function get(target: object, key: string | symbol, receiver: object) {
+    if (key === ReactiveFlags.isReactive) {
+      return !isReadonly
+    } else if (key === ReactiveFlags.isReadonly) {
+      return isReadonly
+    } else if (key === ReactiveFlags.raw) {
+      return target
+    }
+
     const targetIsArray = isArray(target)
     if (targetIsArray && hasOwn(arrayInstrumentations, key)) {
       return Reflect.get(arrayInstrumentations, key, receiver)

packages/reactivity/src/collectionHandlers.ts

@@ -1,4 +1,4 @@
-import { toRaw, reactive, readonly } from './reactive'
+import { toRaw, reactive, readonly, ReactiveFlags } from './reactive'
 import { track, trigger, ITERATE_KEY, MAP_KEY_ITERATE_KEY } from './effect'
 import { TrackOpTypes, TriggerOpTypes } from './operations'
 import {
@@ -242,29 +242,40 @@ iteratorMethods.forEach(method => {
   )
 })
 
-function createInstrumentationGetter(
-  instrumentations: Record<string, Function>
-) {
+function createInstrumentationGetter(isReadonly: boolean) {
+  const instrumentations = isReadonly
+    ? readonlyInstrumentations
+    : mutableInstrumentations
+
   return (
     target: CollectionTypes,
     key: string | symbol,
     receiver: CollectionTypes
-  ) =>
-    Reflect.get(
+  ) => {
+    if (key === ReactiveFlags.isReactive) {
+      return !isReadonly
+    } else if (key === ReactiveFlags.isReadonly) {
+      return isReadonly
+    } else if (key === ReactiveFlags.raw) {
+      return target
+    }
+
+    return Reflect.get(
       hasOwn(instrumentations, key) && key in target
         ? instrumentations
         : target,
       key,
       receiver
     )
+  }
 }
 
 export const mutableCollectionHandlers: ProxyHandler<CollectionTypes> = {
-  get: createInstrumentationGetter(mutableInstrumentations)
+  get: createInstrumentationGetter(false)
 }
 
 export const readonlyCollectionHandlers: ProxyHandler<CollectionTypes> = {
-  get: createInstrumentationGetter(readonlyInstrumentations)
+  get: createInstrumentationGetter(true)
 }
 
 function checkIdentityKeys(

packages/reactivity/src/computed.ts

@@ -57,7 +57,7 @@ export function computed<T>(
     }
   })
   computed = {
-    _isRef: true,
+    __v_isRef: true,
     // expose effect so computed can be stopped
     effect: runner,
     get value() {

packages/reactivity/src/index.ts

@@ -21,7 +21,8 @@ export {
   shallowReactive,
   shallowReadonly,
   markRaw,
-  toRaw
+  toRaw,
+  ReactiveFlags
 } from './reactive'
 export {
   computed,

packages/reactivity/src/reactive.ts

@@ -1,4 +1,4 @@
-import { isObject, toRawType } from '@vue/shared'
+import { isObject, toRawType, def } from '@vue/shared'
 import {
   mutableHandlers,
   readonlyHandlers,
@@ -13,25 +13,38 @@ import { UnwrapRef, Ref } from './ref'
 import { makeMap } from '@vue/shared'
 
 // WeakMaps that store {raw <-> observed} pairs.
-const rawToReactive = new WeakMap<any, any>()
-const reactiveToRaw = new WeakMap<any, any>()
-const rawToReadonly = new WeakMap<any, any>()
-const readonlyToRaw = new WeakMap<any, any>()
+// const rawToReactive = new WeakMap<any, any>()
+// const reactiveToRaw = new WeakMap<any, any>()
+// const rawToReadonly = new WeakMap<any, any>()
+// const readonlyToRaw = new WeakMap<any, any>()
 
-// WeakSets for values that are marked readonly or non-reactive during
-// observable creation.
-const rawValues = new WeakSet<any>()
+export const enum ReactiveFlags {
+  skip = '__v_skip',
+  isReactive = '__v_isReactive',
+  isReadonly = '__v_isReadonly',
+  raw = '__v_raw',
+  reactive = '__v_reactive',
+  readonly = '__v_readonly'
+}
+
+interface Target {
+  __v_skip?: boolean
+  __v_isReactive?: boolean
+  __v_isReadonly?: boolean
+  __v_raw?: any
+  __v_reactive?: any
+  __v_readonly?: any
+}
 
 const collectionTypes = new Set<Function>([Set, Map, WeakMap, WeakSet])
 const isObservableType = /*#__PURE__*/ makeMap(
   'Object,Array,Map,Set,WeakMap,WeakSet'
 )
 
-const canObserve = (value: any): boolean => {
+const canObserve = (value: Target): boolean => {
   return (
-    !value._isVNode &&
+    !value.__v_skip &&
     isObservableType(toRawType(value)) &&
-    !rawValues.has(value) &&
     !Object.isFrozen(value)
   )
 }
@@ -42,13 +55,12 @@ type UnwrapNestedRefs<T> = T extends Ref ? T : UnwrapRef<T>
 export function reactive<T extends object>(target: T): UnwrapNestedRefs<T>
 export function reactive(target: object) {
   // if trying to observe a readonly proxy, return the readonly version.
-  if (readonlyToRaw.has(target)) {
+  if (target && (target as Target).__v_isReadonly) {
     return target
   }
   return createReactiveObject(
     target,
-    rawToReactive,
-    reactiveToRaw,
+    false,
     mutableHandlers,
     mutableCollectionHandlers
   )
@@ -60,8 +72,7 @@ export function reactive(target: object) {
 export function shallowReactive<T extends object>(target: T): T {
   return createReactiveObject(
     target,
-    rawToReactive,
-    reactiveToRaw,
+    false,
     shallowReactiveHandlers,
     mutableCollectionHandlers
   )
@@ -72,8 +83,7 @@ export function readonly<T extends object>(
 ): Readonly<UnwrapNestedRefs<T>> {
   return createReactiveObject(
     target,
-    rawToReadonly,
-    readonlyToRaw,
+    true,
     readonlyHandlers,
     readonlyCollectionHandlers
   )
@@ -88,17 +98,15 @@ export function shallowReadonly<T extends object>(
 ): Readonly<{ [K in keyof T]: UnwrapNestedRefs<T[K]> }> {
   return createReactiveObject(
     target,
-    rawToReadonly,
-    readonlyToRaw,
+    true,
     shallowReadonlyHandlers,
     readonlyCollectionHandlers
   )
 }
 
 function createReactiveObject(
-  target: unknown,
-  toProxy: WeakMap<any, any>,
-  toRaw: WeakMap<any, any>,
+  target: Target,
+  isReadonly: boolean,
   baseHandlers: ProxyHandler<any>,
   collectionHandlers: ProxyHandler<any>
 ) {
@@ -108,15 +116,16 @@ function createReactiveObject(
     }
     return target
   }
+  // target is already a Proxy, return it.
+  // excpetion: calling readonly() on a reactive object
+  if (target.__v_raw && !(isReadonly && target.__v_isReactive)) {
+    return target
+  }
   // target already has corresponding Proxy
-  let observed = toProxy.get(target)
+  let observed = isReadonly ? target.__v_readonly : target.__v_reactive
   if (observed !== void 0) {
     return observed
   }
-  // target is already a Proxy
-  if (toRaw.has(target)) {
-    return target
-  }
   // only a whitelist of value types can be observed.
   if (!canObserve(target)) {
     return target
@@ -125,30 +134,34 @@ function createReactiveObject(
     ? collectionHandlers
     : baseHandlers
   observed = new Proxy(target, handlers)
-  toProxy.set(target, observed)
-  toRaw.set(observed, target)
+  def(
+    target,
+    isReadonly ? ReactiveFlags.readonly : ReactiveFlags.reactive,
+    observed
+  )
   return observed
 }
 
 export function isReactive(value: unknown): boolean {
-  value = readonlyToRaw.get(value) || value
-  return reactiveToRaw.has(value)
+  if (isReadonly(value)) {
+    return isReactive((value as Target).__v_raw)
+  }
+  return !!(value && (value as Target).__v_isReactive)
 }
 
 export function isReadonly(value: unknown): boolean {
-  return readonlyToRaw.has(value)
+  return !!(value && (value as Target).__v_isReadonly)
 }
 
 export function isProxy(value: unknown): boolean {
-  return readonlyToRaw.has(value) || reactiveToRaw.has(value)
+  return isReactive(value) || isReadonly(value)
 }
 
 export function toRaw<T>(observed: T): T {
-  observed = readonlyToRaw.get(observed) || observed
-  return reactiveToRaw.get(observed) || observed
+  return (observed && toRaw((observed as Target).__v_raw)) || observed
 }
 
 export function markRaw<T extends object>(value: T): T {
-  rawValues.add(value)
+  def(value, ReactiveFlags.skip, true)
   return value
 }

packages/reactivity/src/ref.ts

@@ -5,18 +5,11 @@ import { reactive, isProxy, toRaw } from './reactive'
 import { ComputedRef } from './computed'
 import { CollectionTypes } from './collectionHandlers'
 
-const isRefSymbol = Symbol()
-
 export interface Ref<T = any> {
-  // This field is necessary to allow TS to differentiate a Ref from a plain
-  // object that happens to have a "value" field.
-  // However, checking a symbol on an arbitrary object is much slower than
-  // checking a plain property, so we use a _isRef plain property for isRef()
-  // check in the actual implementation.
-  // The reason for not just declaring _isRef in the interface is because we
-  // don't want this internal field to leak into userland autocompletion -
-  // a private symbol, on the other hand, achieves just that.
-  [isRefSymbol]: true
+  /**
+   * @internal
+   */
+  __v_isRef: true
   value: T
 }
 
@@ -27,7 +20,7 @@ const convert = <T extends unknown>(val: T): T =>
 
 export function isRef<T>(r: Ref<T> | unknown): r is Ref<T>
 export function isRef(r: any): r is Ref {
-  return r ? r._isRef === true : false
+  return r ? r.__v_isRef === true : false
 }
 
 export function ref<T extends object>(
@@ -51,7 +44,7 @@ function createRef(rawValue: unknown, shallow = false) {
   }
   let value = shallow ? rawValue : convert(rawValue)
   const r = {
-    _isRef: true,
+    __v_isRef: true,
     get value() {
       track(r, TrackOpTypes.GET, 'value')
       return value
@@ -99,7 +92,7 @@ export function customRef<T>(factory: CustomRefFactory<T>): Ref<T> {
     () => trigger(r, TriggerOpTypes.SET, 'value')
   )
   const r = {
-    _isRef: true,
+    __v_isRef: true,
     get value() {
       return get()
     },
@@ -126,7 +119,7 @@ export function toRef<T extends object, K extends keyof T>(
   key: K
 ): Ref<T[K]> {
   return {
-    _isRef: true,
+    __v_isRef: true,
     get value(): any {
       return object[key]
     },