Rewrite Subscription as a closure factory for byte shaving

.babelrc.js

@@ -12,13 +12,17 @@ module.exports = {
         // Use the equivalent of `babel-preset-modules`
         bugfixes: true,
         modules: false,
+        loose: true,
       },
     ],
     '@babel/preset-typescript',
   ],
   plugins: [
     ['@babel/proposal-decorators', { legacy: true }],
     '@babel/transform-react-jsx',
+    ['@babel/plugin-proposal-class-properties', { loose: true }],
+    ['@babel/plugin-proposal-private-methods', { loose: true }],
+    ['@babel/plugin-proposal-private-property-in-object', { loose: true }],
     cjs && ['@babel/transform-modules-commonjs'],
     [
       '@babel/transform-runtime',

src/components/Context.ts

@@ -1,7 +1,7 @@
 import React from 'react'
 import { Action, AnyAction, Store } from 'redux'
 import type { FixTypeLater } from '../types'
-import type Subscription from '../utils/Subscription'
+import type { Subscription } from '../utils/Subscription'
 
 export interface ReactReduxContextValue<
   SS = FixTypeLater,
@@ -11,9 +11,8 @@ export interface ReactReduxContextValue<
   subscription: Subscription
 }
 
-export const ReactReduxContext = /*#__PURE__*/ React.createContext<ReactReduxContextValue | null>(
-  null
-)
+export const ReactReduxContext =
+  /*#__PURE__*/ React.createContext<ReactReduxContextValue | null>(null)
 
 if (process.env.NODE_ENV !== 'production') {
   ReactReduxContext.displayName = 'ReactRedux'

src/components/Provider.tsx

@@ -1,6 +1,6 @@
 import React, { Context, ReactNode, useMemo } from 'react'
 import { ReactReduxContext, ReactReduxContextValue } from './Context'
-import Subscription from '../utils/Subscription'
+import { createSubscription } from '../utils/Subscription'
 import { useIsomorphicLayoutEffect } from '../utils/useIsomorphicLayoutEffect'
 import type { FixTypeLater } from '../types'
 import { Action, AnyAction, Store } from 'redux'
@@ -21,7 +21,7 @@ interface ProviderProps<A extends Action = AnyAction> {
 
 function Provider({ store, context, children }: ProviderProps) {
   const contextValue = useMemo(() => {
-    const subscription = new Subscription(store)
+    const subscription = createSubscription(store)
     subscription.onStateChange = subscription.notifyNestedSubs
     return {
       store,

src/components/connectAdvanced.js

@@ -1,7 +1,7 @@
 import hoistStatics from 'hoist-non-react-statics'
 import React, { useContext, useMemo, useRef, useReducer } from 'react'
 import { isValidElementType, isContextConsumer } from 'react-is'
-import Subscription from '../utils/Subscription'
+import { createSubscription } from '../utils/Subscription'
 import { useIsomorphicLayoutEffect } from '../utils/useIsomorphicLayoutEffect'
 
 import { ReactReduxContext } from './Context'
@@ -334,7 +334,7 @@ export default function connectAdvanced(
 
         // This Subscription's source should match where store came from: props vs. context. A component
         // connected to the store via props shouldn't use subscription from context, or vice versa.
-        const subscription = new Subscription(
+        const subscription = createSubscription(
           store,
           didStoreComeFromProps ? null : contextValue.subscription
         )
@@ -343,9 +343,8 @@ export default function connectAdvanced(
         // the middle of the notification loop, where `subscription` will then be null. This can
         // probably be avoided if Subscription's listeners logic is changed to not call listeners
         // that have been unsubscribed in the  middle of the notification loop.
-        const notifyNestedSubs = subscription.notifyNestedSubs.bind(
-          subscription
-        )
+        const notifyNestedSubs =
+          subscription.notifyNestedSubs.bind(subscription)
 
         return [subscription, notifyNestedSubs]
       }, [store, didStoreComeFromProps, contextValue])

src/hooks/useSelector.ts

@@ -1,16 +1,16 @@
 import { useReducer, useRef, useMemo, useContext, useDebugValue } from 'react'
 import { useReduxContext as useDefaultReduxContext } from './useReduxContext'
-import Subscription from '../utils/Subscription'
+import { createSubscription, Subscription } from '../utils/Subscription'
 import { useIsomorphicLayoutEffect } from '../utils/useIsomorphicLayoutEffect'
 import { ReactReduxContext } from '../components/Context'
 import { AnyAction, Store } from 'redux'
 import { DefaultRootState } from '../types'
 
-type EqualityFn<T> = (a: T | undefined, b: T | undefined) => boolean;
+type EqualityFn<T> = (a: T | undefined, b: T | undefined) => boolean
 
 const refEquality: EqualityFn<any> = (a, b) => a === b
 
-type TSelector<S, R> = (state: S) => R;
+type TSelector<S, R> = (state: S) => R
 
 function useSelectorWithStoreAndSubscription<TStoreState, TSelectedState>(
   selector: TSelector<TStoreState, TSelectedState>,
@@ -20,10 +20,10 @@ function useSelectorWithStoreAndSubscription<TStoreState, TSelectedState>(
 ): TSelectedState {
   const [, forceRender] = useReducer((s) => s + 1, 0)
 
-  const subscription = useMemo(() => new Subscription(store, contextSub), [
-    store,
-    contextSub,
-  ])
+  const subscription = useMemo(
+    () => createSubscription(store, contextSub),
+    [store, contextSub]
+  )
 
   const latestSubscriptionCallbackError = useRef<Error>()
   const latestSelector = useRef<TSelector<TStoreState, TSelectedState>>()
@@ -107,13 +107,21 @@ function useSelectorWithStoreAndSubscription<TStoreState, TSelectedState>(
  * @param {React.Context} [context=ReactReduxContext] Context passed to your `<Provider>`.
  * @returns {Function} A `useSelector` hook bound to the specified context.
  */
-export function createSelectorHook(context = ReactReduxContext): <TState = DefaultRootState, Selected = unknown>(selector: (state: TState) => Selected, equalityFn?: EqualityFn<Selected>) => Selected {
+export function createSelectorHook(
+  context = ReactReduxContext
+): <TState = DefaultRootState, Selected = unknown>(
+  selector: (state: TState) => Selected,
+  equalityFn?: EqualityFn<Selected>
+) => Selected {
   const useReduxContext =
     context === ReactReduxContext
       ? useDefaultReduxContext
       : () => useContext(context)
-
-  return function useSelector<TState, Selected extends unknown>(selector: (state: TState) => Selected, equalityFn: EqualityFn<Selected> = refEquality): Selected {
+
+  return function useSelector<TState, Selected extends unknown>(
+    selector: (state: TState) => Selected,
+    equalityFn: EqualityFn<Selected> = refEquality
+  ): Selected {
     if (process.env.NODE_ENV !== 'production') {
       if (!selector) {
         throw new Error(`You must pass a selector to useSelector`)

src/utils/Subscription.ts

@@ -4,8 +4,10 @@ import { getBatch } from './batch'
 // well as nesting subscriptions of descendant components, so that we can ensure the
 // ancestor components re-render before descendants
 
+type VoidFunc = () => void
+
 type Listener = {
-  callback: () => void
+  callback: VoidFunc
   next: Listener | null
   prev: Listener | null
 }
@@ -77,55 +79,73 @@ function createListenerCollection() {
 
 type ListenerCollection = ReturnType<typeof createListenerCollection>
 
-export default class Subscription {
-  private store: any
-  private parentSub?: Subscription
-  private unsubscribe?: () => void
-  private listeners?: ListenerCollection
-  public onStateChange?: () => void
+export interface Subscription {
+  addNestedSub: (listener: VoidFunc) => VoidFunc
+  notifyNestedSubs: VoidFunc
+  handleChangeWrapper: VoidFunc
+  isSubscribed: () => boolean
+  onStateChange?: VoidFunc
+  trySubscribe: VoidFunc
+  tryUnsubscribe: VoidFunc
+  getListeners: () => ListenerCollection
+}
 
-  constructor(store: any, parentSub?: Subscription) {
-    this.store = store
-    this.parentSub = parentSub
-    this.unsubscribe = undefined
-    this.listeners = undefined
+const nullListeners = {
+  notify() {},
+  get: () => [],
+} as unknown as ListenerCollection
 
-    this.handleChangeWrapper = this.handleChangeWrapper.bind(this)
-  }
+export function createSubscription(store: any, parentSub?: Subscription) {
+  let unsubscribe: VoidFunc | undefined
+  let listeners: ListenerCollection = nullListeners
 
-  addNestedSub(listener: () => void) {
-    this.trySubscribe()
-    return this.listeners?.subscribe(listener)
+  function addNestedSub(listener: () => void) {
+    trySubscribe()
+    return listeners.subscribe(listener)
   }
 
-  notifyNestedSubs() {
-    this.listeners?.notify()
+  function notifyNestedSubs() {
+    listeners.notify()
   }
 
-  handleChangeWrapper() {
-    this.onStateChange?.()
+  function handleChangeWrapper() {
+    if (subscription.onStateChange) {
+      subscription.onStateChange()
+    }
   }
 
-  isSubscribed() {
-    return Boolean(this.unsubscribe)
+  function isSubscribed() {
+    return Boolean(unsubscribe)
   }
 
-  trySubscribe() {
-    if (!this.unsubscribe) {
-      this.unsubscribe = this.parentSub
-        ? this.parentSub.addNestedSub(this.handleChangeWrapper)
-        : this.store.subscribe(this.handleChangeWrapper)
+  function trySubscribe() {
+    if (!unsubscribe) {
+      unsubscribe = parentSub
+        ? parentSub.addNestedSub(handleChangeWrapper)
+        : store.subscribe(handleChangeWrapper)
 
-      this.listeners = createListenerCollection()
+      listeners = createListenerCollection()
     }
   }
 
-  tryUnsubscribe() {
-    if (this.unsubscribe) {
-      this.unsubscribe()
-      this.unsubscribe = undefined
-      this.listeners?.clear()
-      this.listeners = undefined
+  function tryUnsubscribe() {
+    if (unsubscribe) {
+      unsubscribe()
+      unsubscribe = undefined
+      listeners.clear()
+      listeners = nullListeners
     }
   }
+
+  const subscription: Subscription = {
+    addNestedSub,
+    notifyNestedSubs,
+    handleChangeWrapper,
+    isSubscribed,
+    trySubscribe,
+    tryUnsubscribe,
+    getListeners: () => listeners,
+  }
+
+  return subscription
 }

src/utils/bindActionCreators.ts

@@ -1,28 +1,10 @@
-import {
-  ActionCreator,
-  ActionCreatorsMapObject,
-  AnyAction,
-  Dispatch,
-} from 'redux'
-
-function bindActionCreator<A extends AnyAction = AnyAction>(
-  actionCreator: ActionCreator<A>,
-  dispatch: Dispatch
-) {
-  return function (this: any, ...args: any[]) {
-    return dispatch(actionCreator.apply(this, args))
-  }
-}
+import { ActionCreatorsMapObject, Dispatch } from 'redux'
 
 export default function bindActionCreators(
-  actionCreators: ActionCreator<any> | ActionCreatorsMapObject,
+  actionCreators: ActionCreatorsMapObject,
   dispatch: Dispatch
 ) {
-  if (typeof actionCreators === 'function') {
-    return bindActionCreator(actionCreators, dispatch)
-  }
-
-  const boundActionCreators: ActionCreatorsMapObject = {}
+  const boundActionCreators: ActionCreatorsMapObject<any> = {}
   for (const key in actionCreators) {
     const actionCreator = actionCreators[key]
     if (typeof actionCreator === 'function') {

test/hooks/useSelector.spec.js

@@ -101,11 +101,11 @@ describe('React', () => {
             </ProviderMock>
           )
 
-          expect(rootSubscription.listeners.get().length).toBe(1)
+          expect(rootSubscription.getListeners().get().length).toBe(1)
 
           store.dispatch({ type: '' })
 
-          expect(rootSubscription.listeners.get().length).toBe(2)
+          expect(rootSubscription.getListeners().get().length).toBe(2)
         })
 
         it('unsubscribes when the component is unmounted', () => {
@@ -129,11 +129,11 @@ describe('React', () => {
             </ProviderMock>
           )
 
-          expect(rootSubscription.listeners.get().length).toBe(2)
+          expect(rootSubscription.getListeners().get().length).toBe(2)
 
           store.dispatch({ type: '' })
 
-          expect(rootSubscription.listeners.get().length).toBe(1)
+          expect(rootSubscription.getListeners().get().length).toBe(1)
         })
 
         it('notices store updates between render and store subscription effect', () => {

test/utils/Subscription.spec.js

@@ -1,4 +1,4 @@
-import Subscription from '../../src/utils/Subscription'
+import { createSubscription } from '../../src/utils/Subscription'
 
 describe('Subscription', () => {
   let notifications
@@ -9,13 +9,13 @@ describe('Subscription', () => {
     notifications = []
     store = { subscribe: () => jest.fn() }
 
-    parent = new Subscription(store)
+    parent = createSubscription(store)
     parent.onStateChange = () => {}
     parent.trySubscribe()
   })
 
   function subscribeChild(name) {
-    const child = new Subscription(store, parent)
+    const child = createSubscription(store, parent)
     child.onStateChange = () => notifications.push(name)
     child.trySubscribe()
     return child