WHAT I HAVE
LEARNED FROM
REDUX SOURCE CODE

Source Code

Why Redux

  • less code
  • skillfully
  • cool

Redux

State Management

  1. components communication
  2. fetch API && store data
  3. form
  1. middleware 
  2. redux-form

use case

library

The global state of your application is stored in an object tree within a single store

  1. components communication
  2. fetch API && store data
  3. form

use case

context

Apollo cache

final form ?!

State Management

The global state of your application is stored in an object tree within a single store

Redux

import redux from 'redux';

const initialState = {
  counter: 0
}

// Reducer
const rootReducer = ( state = initialState, action) => {
  if(action.type === 'INC_COUNTER'){
    return {
      ...state,
      counter: state.counter + 1
    }
  }
  if(action.type === 'ADD_COUNTER'){
    return {
      ...state,
      counter: state.counter + action.value
    }
  }
  retrun state;
}

// Store
const store = redux.createStore(rootReducer)
console.log(store.getState())

// Subscription
store.subscribe(() => {
  console.log('[Subscription]', store.getState())
});


// Dispatching Action
store.dispatch({type: 'INC_COUNTER'});
store.dispatch({type: 'ADD_COUNTER', value: 10});
console.log(store.getState());

Basic

function AppraiseTaskFormProgramPickupTable() {
  ...
}


const reduxHook = connect(
  state => ({
    fetchLimit: state.Table.fetchLimit,
    pickedPrograms: selectorFromMainTable(state, 'programs') || [],
  }),
  dispatch => bindActionCreators({
    addProgram: programId => arrayPush(FORM_APPRAISE_TASK_PROGRAM_PICKER, 'programs', programId),
    removeProgramAtIndex: index => arrayRemove(FORM_APPRAISE_TASK_PROGRAM_PICKER, 'programs', index),
  }, dispatch),
);

export default compose(
  withRouter,
  reduxHook,
)(AppraiseTaskFormProgramPickupTable);

React-redux

  • Scalable
  • functional
  • curry
  • recursive

Redux Source Code

import {
  createStore,
  combineReducers,
  compose,
  applyMiddleware,
} from 'redux';
import thunk from 'redux-thunk';
import { reducer as form } from 'redux-form';
import { createBrowserHistory } from 'history';
import {
  connectRouter,
  routerMiddleware,
} from 'connected-react-router';
import Table from './reducers/Table';
import Card from './reducers/Card';

export const history = createBrowserHistory();

const store = createStore(combineReducers({
  Card,
  Table,
  form,
  router: connectRouter(history),
}), {}, compose(
  applyMiddleware(
    thunk,
    routerMiddleware(history),
  ),
));

export default store;
  • Scalable
  • functional
  • curry
  • recursive

Redux Source Code

import {
  createStore,
  combineReducers,
  compose,
  applyMiddleware,
} from 'redux';
import thunk from 'redux-thunk';
import { reducer as form } from 'redux-form';
import { createBrowserHistory } from 'history';
import {
  connectRouter,
  routerMiddleware,
} from 'connected-react-router';
import Table from './reducers/Table';
import Card from './reducers/Card';

export const history = createBrowserHistory();

const store = createStore(combineReducers({
  Card,
  Table,
  form,
  router: connectRouter(history),
}), {}, compose(
  applyMiddleware(
    thunk,
    routerMiddleware(history),
  ),
));

export default store;
  • Scalable
  • functional
  • curry
  • recursive

Redux Source Code

import {
  createStore,
  combineReducers,
  compose,
  applyMiddleware,
} from 'redux';
import thunk from 'redux-thunk';
import { reducer as form } from 'redux-form';
import { createBrowserHistory } from 'history';
import {
  connectRouter,
  routerMiddleware,
} from 'connected-react-router';
import Table from './reducers/Table';
import Card from './reducers/Card';

export const history = createBrowserHistory();

const store = createStore(combineReducers({
  Card,
  Table,
  form,
  router: connectRouter(history),
}), {}, compose(
  applyMiddleware(
    thunk,
    routerMiddleware(history),
  ),
));

export default store;

// 4.05
src
├── applyMiddleware.js  
├── bindActionCreators.js  
├── combineReducers.js  
├── compose.js  
├── createStore.js  
├── index.js    
└── utils   
    ├── actionTypes.js  
    ├── isPlainObject.js  
    └── warning.js

struture

import $$observable from 'symbol-observable'

import ActionTypes from './utils/actionTypes'
import isPlainObject from './utils/isPlainObject'

export default function createStore(reducer, preloadedState, enhancer) {
  if (
    (typeof preloadedState === 'function' && typeof enhancer === 'function') ||
    (typeof enhancer === 'function' && typeof arguments[3] === 'function')
  ) {
    throw new Error(
      'It looks like you are passing several store enhancers to ' +
        'createStore(). This is not supported. Instead, compose them ' +
        'together to a single function.'
    )
  }

  if (typeof preloadedState === 'function' && typeof enhancer === 'undefined') {
    enhancer = preloadedState
    preloadedState = undefined
  }

  if (typeof enhancer !== 'undefined') {
    if (typeof enhancer !== 'function') {
      throw new Error('Expected the enhancer to be a function.')
    }

    return enhancer(createStore)(reducer, preloadedState)
  }

  if (typeof reducer !== 'function') {
    throw new Error('Expected the reducer to be a function.')
  }

  let currentReducer = reducer
  let currentState = preloadedState
  let currentListeners = []
  let nextListeners = currentListeners
  let isDispatching = false

  function ensureCanMutateNextListeners() {
    if (nextListeners === currentListeners) {
      nextListeners = currentListeners.slice()
    }
  }

  function getState() {
    if (isDispatching) {
      throw new Error(
        'You may not call store.getState() while the reducer is executing. ' +
          'The reducer has already received the state as an argument. ' +
          'Pass it down from the top reducer instead of reading it from the store.'
      )
    }

    return currentState
  }

  function subscribe(listener) {
    if (typeof listener !== 'function') {
      throw new Error('Expected the listener to be a function.')
    }

    if (isDispatching) {
      throw new Error(
        'You may not call store.subscribe() while the reducer is executing. ' +
          'If you would like to be notified after the store has been updated, subscribe from a ' +
          'component and invoke store.getState() in the callback to access the latest state. ' +
          'See https://redux.js.org/api-reference/store#subscribelistener for more details.'
      )
    }

    let isSubscribed = true

    ensureCanMutateNextListeners()
    nextListeners.push(listener)

    return function unsubscribe() {
      if (!isSubscribed) {
        return
      }

      if (isDispatching) {
        throw new Error(
          'You may not unsubscribe from a store listener while the reducer is executing. ' +
            'See https://redux.js.org/api-reference/store#subscribelistener for more details.'
        )
      }

      isSubscribed = false

      ensureCanMutateNextListeners()
      const index = nextListeners.indexOf(listener)
      nextListeners.splice(index, 1)
      currentListeners = null
    }
  }
  
  function dispatch(action) {
    if (!isPlainObject(action)) {
      throw new Error(
        'Actions must be plain objects. ' +
          'Use custom middleware for async actions.'
      )
    }

    if (typeof action.type === 'undefined') {
      throw new Error(
        'Actions may not have an undefined "type" property. ' +
          'Have you misspelled a constant?'
      )
    }

    if (isDispatching) {
      throw new Error('Reducers may not dispatch actions.')
    }

    try {
      isDispatching = true
      currentState = currentReducer(currentState, action)
    } finally {
      isDispatching = false
    }

    const listeners = (currentListeners = nextListeners)
    for (let i = 0; i < listeners.length; i++) {
      const listener = listeners[i]
      listener()
    }

    return action
  }

  function replaceReducer(nextReducer) {
    if (typeof nextReducer !== 'function') {
      throw new Error('Expected the nextReducer to be a function.')
    }

    currentReducer = nextReducer

    dispatch({ type: ActionTypes.REPLACE })
  }

  dispatch({ type: ActionTypes.INIT })

  return {
    dispatch,
    subscribe,
    getState,
    replaceReducer,
  }
}

createStore

import $$observable from 'symbol-observable'

import ActionTypes from './utils/actionTypes'
import isPlainObject from './utils/isPlainObject'

export default function createStore(reducer, preloadedState, enhancer) {
  if (
    (typeof preloadedState === 'function' && typeof enhancer === 'function') ||
    (typeof enhancer === 'function' && typeof arguments[3] === 'function')
  ) {
    throw new Error(
      'It looks like you are passing several store enhancers to ' +
        'createStore(). This is not supported. Instead, compose them ' +
        'together to a single function.'
    )
  }

  if (typeof preloadedState === 'function' && typeof enhancer === 'undefined') {
    enhancer = preloadedState
    preloadedState = undefined
  }

  if (typeof enhancer !== 'undefined') {
    if (typeof enhancer !== 'function') {
      throw new Error('Expected the enhancer to be a function.')
    }

    return enhancer(createStore)(reducer, preloadedState)
  }

  if (typeof reducer !== 'function') {
    throw new Error('Expected the reducer to be a function.')
  }

  let currentReducer = reducer
  let currentState = preloadedState
  let currentListeners = []
  let nextListeners = currentListeners
  let isDispatching = false

  function ensureCanMutateNextListeners() {
    if (nextListeners === currentListeners) {
      nextListeners = currentListeners.slice()
    }
  }

  function getState() {
    if (isDispatching) {
      throw new Error(
        'You may not call store.getState() while the reducer is executing. ' +
          'The reducer has already received the state as an argument. ' +
          'Pass it down from the top reducer instead of reading it from the store.'
      )
    }

    return currentState
  }

  function subscribe(listener) {
    if (typeof listener !== 'function') {
      throw new Error('Expected the listener to be a function.')
    }

    if (isDispatching) {
      throw new Error(
        'You may not call store.subscribe() while the reducer is executing. ' +
          'If you would like to be notified after the store has been updated, subscribe from a ' +
          'component and invoke store.getState() in the callback to access the latest state. ' +
          'See https://redux.js.org/api-reference/store#subscribelistener for more details.'
      )
    }

    let isSubscribed = true

    ensureCanMutateNextListeners()
    nextListeners.push(listener)

    return function unsubscribe() {
      if (!isSubscribed) {
        return
      }

      if (isDispatching) {
        throw new Error(
          'You may not unsubscribe from a store listener while the reducer is executing. ' +
            'See https://redux.js.org/api-reference/store#subscribelistener for more details.'
        )
      }

      isSubscribed = false

      ensureCanMutateNextListeners()
      const index = nextListeners.indexOf(listener)
      nextListeners.splice(index, 1)
      currentListeners = null
    }
  }
  
  function dispatch(action) {
    if (!isPlainObject(action)) {
      throw new Error(
        'Actions must be plain objects. ' +
          'Use custom middleware for async actions.'
      )
    }

    if (typeof action.type === 'undefined') {
      throw new Error(
        'Actions may not have an undefined "type" property. ' +
          'Have you misspelled a constant?'
      )
    }

    if (isDispatching) {
      throw new Error('Reducers may not dispatch actions.')
    }

    try {
      isDispatching = true
      currentState = currentReducer(currentState, action)
    } finally {
      isDispatching = false
    }

    const listeners = (currentListeners = nextListeners)
    for (let i = 0; i < listeners.length; i++) {
      const listener = listeners[i]
      listener()
    }

    return action
  }

  function replaceReducer(nextReducer) {
    if (typeof nextReducer !== 'function') {
      throw new Error('Expected the nextReducer to be a function.')
    }

    currentReducer = nextReducer

    dispatch({ type: ActionTypes.REPLACE })
  }

  dispatch({ type: ActionTypes.INIT })

  return {
    dispatch,
    subscribe,
    getState,
    replaceReducer,
  }
}

createStore

import {
  createStore,
  combineReducers,
  compose,
  applyMiddleware,
} from 'redux';
import thunk from 'redux-thunk';
import { reducer as form } from 'redux-form';
import { createBrowserHistory } from 'history';
import {
  connectRouter,
  routerMiddleware,
} from 'connected-react-router';
import Table from './reducers/Table';
import Card from './reducers/Card';

export const history = createBrowserHistory();

const store = createStore(combineReducers({
  Card,
  Table,
  form,
  router: connectRouter(history),
}), {}, compose(
  applyMiddleware(
    thunk,
    routerMiddleware(history),
  ),
));

export default store;

import $$observable from 'symbol-observable'

import ActionTypes from './utils/actionTypes'
import isPlainObject from './utils/isPlainObject'

export default function createStore(reducer, preloadedState, enhancer) {
  if (
    (typeof preloadedState === 'function' && typeof enhancer === 'function') ||
    (typeof enhancer === 'function' && typeof arguments[3] === 'function')
  ) {
    throw new Error(
      'It looks like you are passing several store enhancers to ' +
        'createStore(). This is not supported. Instead, compose them ' +
        'together to a single function.'
    )
  }

  if (typeof preloadedState === 'function' && typeof enhancer === 'undefined') {
    enhancer = preloadedState
    preloadedState = undefined
  }

  if (typeof enhancer !== 'undefined') {
    if (typeof enhancer !== 'function') {
      throw new Error('Expected the enhancer to be a function.')
    }

    return enhancer(createStore)(reducer, preloadedState)
  }

  if (typeof reducer !== 'function') {
    throw new Error('Expected the reducer to be a function.')
  }

  let currentReducer = reducer
  let currentState = preloadedState
  let currentListeners = []
  let nextListeners = currentListeners
  let isDispatching = false

  function ensureCanMutateNextListeners() {
    if (nextListeners === currentListeners) {
      nextListeners = currentListeners.slice()
    }
  }

  function getState() {
    if (isDispatching) {
      throw new Error(
        'You may not call store.getState() while the reducer is executing. ' +
          'The reducer has already received the state as an argument. ' +
          'Pass it down from the top reducer instead of reading it from the store.'
      )
    }

    return currentState
  }

  function subscribe(listener) {
    if (typeof listener !== 'function') {
      throw new Error('Expected the listener to be a function.')
    }

    if (isDispatching) {
      throw new Error(
        'You may not call store.subscribe() while the reducer is executing. ' +
          'If you would like to be notified after the store has been updated, subscribe from a ' +
          'component and invoke store.getState() in the callback to access the latest state. ' +
          'See https://redux.js.org/api-reference/store#subscribelistener for more details.'
      )
    }

    let isSubscribed = true

    ensureCanMutateNextListeners()
    nextListeners.push(listener)

    return function unsubscribe() {
      if (!isSubscribed) {
        return
      }

      if (isDispatching) {
        throw new Error(
          'You may not unsubscribe from a store listener while the reducer is executing. ' +
            'See https://redux.js.org/api-reference/store#subscribelistener for more details.'
        )
      }

      isSubscribed = false

      ensureCanMutateNextListeners()
      const index = nextListeners.indexOf(listener)
      nextListeners.splice(index, 1)
      currentListeners = null
    }
  }
  
  function dispatch(action) {
    if (!isPlainObject(action)) {
      throw new Error(
        'Actions must be plain objects. ' +
          'Use custom middleware for async actions.'
      )
    }

    if (typeof action.type === 'undefined') {
      throw new Error(
        'Actions may not have an undefined "type" property. ' +
          'Have you misspelled a constant?'
      )
    }

    if (isDispatching) {
      throw new Error('Reducers may not dispatch actions.')
    }

    try {
      isDispatching = true
      currentState = currentReducer(currentState, action)
    } finally {
      isDispatching = false
    }

    const listeners = (currentListeners = nextListeners)
    for (let i = 0; i < listeners.length; i++) {
      const listener = listeners[i]
      listener()
    }

    return action
  }

  function replaceReducer(nextReducer) {
    if (typeof nextReducer !== 'function') {
      throw new Error('Expected the nextReducer to be a function.')
    }

    currentReducer = nextReducer

    dispatch({ type: ActionTypes.REPLACE })
  }

  dispatch({ type: ActionTypes.INIT })

  return {
    dispatch,
    subscribe,
    getState,
    replaceReducer,
  }
}

createStore

export default function applyMiddleware(...middlewares) {
  return createStore => (reducer, ...args) => {
    const store = createStore(reducer, ...args)
    let dispatch = () => {
      throw new Error(
        `Dispatching while constructing your middleware is not allowed. ` +
          `Other middleware would not be applied to this dispatch.`
      )
    }

    const middlewareAPI = {
      getState: store.getState,
      dispatch: (action, ...args) => dispatch(action, ...args)
    }
    const chain = middlewares.map(middleware => middleware(middlewareAPI))
    dispatch = compose(...chain)(store.dispatch)

    return {
      ...store,
      dispatch
    }
  }
}

applyMiddleware

compose

export default function compose(...funcs) {
  if (funcs.length === 0) {
    return arg => arg
  }

  if (funcs.length === 1) {
    return funcs[0]
  }

  return funcs.reduce((a, b) => (...args) => a(b(...args)))
}

Back To The Basic

ES6 

curry

recursive

function foo(otherArg, ...args) {
  console.log(otherArg); //1
  console.log(args); // [2, 3]
}

foo(1,2,3)

ES6 destructing

curry

const add = (x, y) => x + y;

add(9, 8); //17

// create a high-order function
const createAdder = a => b => add(a, b);
const add2 = createAdder(9);

add2(8); // 17
export default function compose(...funcs) {
  if (funcs.length === 0) {
    return arg => arg
  }

  if (funcs.length === 1) {
    return funcs[0]
  }

  return funcs.reduce((a, b) => (...args) => a(b(...args)))
}

Redux.compose

export default function compose(...funcs) {
  return funcs.reduce(
    (accum, curr) => (...args) => accum(curr(...args))
  )
}
const foo = arg => arg * 5
const bar = arg => arg + 2

const calculate = compose(foo, bar)(19)
export default function compose(...funcs) {
  // funcs = [foo, bar]
  return funcs.reduce(
    (accum, curr) => (...args) => accum(curr(...args))
  )
}


// first 
arg => foo(arg)

// second
arg => foo(bar(arg))
const foo = arg => arg * 5
const bar = arg => arg + 2

console.log(compose(foo, bar)(17))
const foo = arg => arg * 5
const bar = arg => arg + 2

console.log(compose(foo, bar)(17)) // 95

recursive

溫故知新 - 淺入淺出 useMemo

function fibonacci (position) {
  if (position <= 2) {
	// break
    return 1
  } else {
    return fibonacci(position - 1) + fibonacci(position - 2)
  }
}

fibonacci(6)   // 5, fibonacci(4) + fibonacci(3)

function createStore(reducer, preloadedState, enhancer) {
  ...
  if (typeof enhancer !== 'undefined') {
      if (typeof enhancer !== 'function') {
        throw new Error('Expected the enhancer to be a function.')
      }

      return enhancer(createStore)(reducer, preloadedState)
    }
  }
  ...
}

Redux.CreateStore

export default function applyMiddleware(...middlewares) {
  return createStore => (reducer, ...args) => {
    const store = createStore(reducer, ...args);
    let dispatch: Dispatch = () => {
      throw new Error(
        'Dispatching while constructing your middleware is not allowed. ' +
          'Other middleware would not be applied to this dispatch.'
      )
    }
    
    const middlewareAPI = {
      getState: store.getState,
      dispatch: (action, ...args) => dispatch(action, ...args)
    };
    const chain = middlewares.map(middleware => middleware(middlewareAPI));
    dispatch = compose(...chain)(store.dispatch);

    return {
      ...store,
      dispatch
    };
  };
}

function createStore(reducer, preloadedState, enhancer) {
  ...
  if (typeof enhancer !== 'undefined') {
      if (typeof enhancer !== 'function') {
        throw new Error('Expected the enhancer to be a function.')
      }

      return enhancer(createStore)(reducer, preloadedState)
    }
  }
  ...
}


export default function applyMiddleware(...middlewares) {
  return createStore => (reducer, ...args) => {
    const store = createStore(reducer, ...args)
    
    ...

    return {
      ...store,
      dispatch
    }
  }
}

// excute
(createStore) => (reducer, ...args) => {...store, dispatch}

applyMiddleware(...middlewares)

enhancer(createStore)(reducer, preloadedState)

(reducer, ...args)

export default function createStore(reducer, preloadedState, enhancer) {
  ...
  /* args' type did not match these condition*/
  ...

  
  let currentReducer = reducer;
  let currentState = preloadedState;

  function getState() {
    return currentState;
  }

  function dispatch(action: A) {
    currentState = currentReducer(currentState, action);
    return action;
  }

  dispatch({ type: ActionTypes.INIT });

  const store = {
    dispatch,
    subscribe,
    getState
  };
  return store;
}

return store

function createStore(...args) {
  const store = {
    dispatch,
    subscribe,
    getState
  };
  return store;
}
export default function applyMiddleware(...middlewares) {
  return createStore => (reducer, ...args) => {
    const store = createStore(reducer, ...args)
    let dispatch = () => {
      throw new Error(
        'Dispatching while constructing your middleware is not allowed. ' +
          'Other middleware would not be applied to this dispatch.'
      )
    }

    const middlewareAPI = {
      getState: store.getState,
      dispatch: (action, ...args) => dispatch(action, ...args)
    }
    const chain = middlewares.map(middleware => middleware(middlewareAPI))
    dispatch = compose(...chain)(store.dispatch)

    return {
      ...store,
      dispatch
    }
  }
}

Redux.applymiddleware

enhance dispatch

middelware

// redux-thunk
function createThunkMiddleware(extraArgument) {
  return ({ dispatch, getState }) => (next) => (action) => {
    if (typeof action === 'function') {
      return action(dispatch, getState, extraArgument);
    }

    return next(action);
  };
}
const middleware = store => next => action => {
  /* Code */
  return next(action);
}
export default function applyMiddleware(...middlewares) {
  return createStore => (reducer, ...args) => {
	... 

    const middlewareAPI = {
      getState: store.getState,
      dispatch: (action, ...args) => dispatch(action, ...args)
    }
    const chain = middlewares.map(middleware => middleware(middlewareAPI))
    dispatch = compose(...chain)(store.dispatch)

    return {
      ...store,
      dispatch
    }
  }
}
const middleware = store => next => action => {
  /* Code */
  return next(action);
}

Why do we need "next"

export default function applyMiddleware(...middlewares) {
  return createStore => (...args) => {
	... 

    const middlewareAPI = {
      getState: store.getState,
      dispatch: (...args) => dispatch(...args)
    }
    const chain = middlewares.map(middleware => middleware(middlewareAPI))

    dispatch = compose(...chain)(store.dispatch)

    return {
      ...store,
      dispatch
    }
  }
}
//chain
const [mw1, mw2]  = middlewares.map(middleware => middleware(middlewareAPI))

//mw1
function (next) => action => {
  ...
  return next(action)
}
export default function applyMiddleware(...middlewares) {
  return createStore => (...args) => {
	... 

    const middlewareAPI = {
      getState: store.getState,
      dispatch: (...args) => dispatch(...args)
    }
    const chain = middlewares.map(middleware => middleware(middlewareAPI))

    dispatch = compose(...chain)(store.dispatch)

    return {
      ...store,
      dispatch
    }
  }
}
const [mw1, mw2]  = middlewares.map(middleware => middleware(middlewareAPI))

// compose(...chain)
next => mw1(mw2(next))
// compose(...chain)(store.dispatch)
mw1(mw2(store.dispatch))
const mw2 = next => action => {
  /* Code */
  return next(action);
}

// mw2(store.dispatch)
action => store.dispatch(action)

// mw1(mw2(store.dispatch))
action =>  mw2(action)

One more thing

https://deno.land/

security

linux-like

have access

to system calls 

package

url

package.json

API

same as browser

basic

微 DEMO

Another thing

Copy Link(HackMD)

What I have learned from redux source code

By Jay Chou

Made with Slides.com

What I have learned from redux source code

  • 486

More from Jay Chou