原文地址： http://qinfanpeng.github.io/jekyll/update/2017/01/03/redux_actions_and_redux_thunk.html

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Agenda

• FSA
• Action Creator
• redux-actions
• redux-promise
• redux-thunk

[slide]

Agenda

• FSA
• Action Creator
• redux-actions
• redux-promise
• redux-thunk

[slide]

Rails REST Routes

---

HTTP Verb	Path	Controller#Action	Used for
GET	/todos	todos#index	display a list of all todos
GET	/todos/new	todos#new	return an HTML form for creating a new todo
POST	/todos	todos#create	create a new todo
GET	/todos/:id	todos#show	display a specific todo
GET	/todos/:id/edit	todos#edit	return an HTML form for editing a todo
PATCH/PUT	/todos/:id	todos#update	update a specific todo
DELETE	/todos/:id	todos#destroy	delete a specific todo

[note] Restul 中由 Http Verb 和 Path 共同决定“要做什么” [/note]

[slide]

Rails Controller & Actions

class TodosController < ApplicationController
  # GET /todos
  def index
    @todos = Todo.all
  end

  # GET /todos/:id
  def show
    @todo = Todo.find(params[:id])
  end

  # GET /todos/new
  def new
    @todo = Todo.new
  end

  # POST /todos
  def create
    @todo = Todo.new(params[:todo])

    if @todo.save
      redirect_to @todo
    else
      render 'new'
    end  
  end

  # ...
end 

[note] Controller 中的 Action 可以从 params 中获取 http 参数。 结合起来看，Flux 中的 Action 要做的事情也极其类似：

1. 决定“要做什么”
2. 携带必要的参数 [/note]

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Describe Redux Action in One Sentence

• What to do ? {:&.fadeIn}
• And along with necessary data

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FSA(Flux Standard Action)

{
  type: ADD_TODO,
  payload: {
    text: 'Do something.'  
  }
}

{
  type: ADD_TODO,
  payload: new Error(),
  error: true
}

[slide]

Flux Standard Action Specifications

• An action MUST {:&.fadeIn}

  • be a plain JavaScript object. {:&.fadeIn}
  • have a type property.

• An action MAY have:

  • an error property. {:&.fadeIn}
  • a payload property.
  • a meta property.

• An action MUST NOT include properties other than type, payload, error, and meta.

[slide]

Benefit of using FSA

• Standard to Follow {:&.fadeIn}
• Easy to switch Flux implementations
• More friendly to middleware

[slide]

Use Action Literal Directly

• {:&.fadeIn}

store.dispatch({
  type: ADD_TODO,
  payload: {
    text: 'Do one thing.'  
  }
})

store.dispatch({
  type: ADD_TODO,
  payload: {
    text: 'Do another thing.'  
  }
})

[note] 直接使用 Action 字面量虽然直接，但繁琐、重复、极像样板（Boilerplate）、代码将代码的主要目的淹没在了细节中（暴露了不必要的细节） [/note]

[slide]

Encapsulate Action in Action Creator

• {:&.fadeIn}

const addTodo = (text) => {
  return {
    type: ADD_TODO,
    payload: { text }
  }  
}

store.dispatch(addTodo('Do one thing.'))
store.dispatch(addTodo('Do another thing.'))

[note] 利用 Action Creator 封装了细节，减少重复，且令调用代码的意图一目了然。 [/note]

[slide]

Todo Actions (by Action Creators)

• {:&.fadeIn}

const addTodo = (text) => {
  return {
    type: ADD_TODO,
    payload: { id: uuid.v4(), text }
  }
}

const updateTodo = (id, text) => {
  return {
    type: UPDATE_TODO,
    payload: { id, text }
  }
}

const clearTodos = () => {
  return {type: CLEAR_TODOS}
}

[note] 即使采用了 Action Creator，但还是有重复的影子，不够完美。 [/note]

[slide]

Use redux-actions to Simplify Action Creator

• {:&.fadeIn}

// Solution One, which is perfer
const addTodo = (text) => {
  return createAction(ADD_TODO)({ id: uuid.v4(), text })
}
store.dispatch(addTodo(1, 'Do something'))

// Solution Two
const addTodo = createAction(ADD_TODO)
store.dispatch(addTodo({id: uuid.v4(), text: 'Do something'}))

const updateTodo = (id, text) => {
  return createAction(UPDATE_TODO)({ id, text })
}

const clearTodos = createAction(CLEAR_TODOS_TODO)
store.dispatch(clearTodos())

[note] 借助 redux-actions 的 createAction 进一步消除重复，简化代码。 [/note]

[slide]

Common Misuse of redux-actions

• {:&.fadeIn}

const deleteTodo = (id) => {
  return createAction(DELETE_TODO)(id)
}

// Same as
const deleteTodo = (id) => {
  return {
    type: DELETE_TODO,
    payload: id
  }
}

const todos = handleActions({
  [DELETE_TODO]: (state, { payload }) => {
    // What the hell is payload ?
    return deleteTodo(state, payload)
  },
}, [])

[note] payload 中的数据应该有自己的结构，而非直接塞给 payload，否则的话，reducer 里代码根本不知道 payload 里有啥。 [/note]

[slide]

the Way to use redux-actions

• {:&.fadeIn}

const deleteTodo = (id) => {
  return createAction('DELETE_TODO')({ id })
}

const todos = handleActions({
  DELETE_TODO: (state, { payload }) => {
    return deleteTodo(state, payload.id)
  },
}, [])

[slide]

use redux-promise to Call API

const fetchTodo = (id) => {
  return {
    type: 'FETCH_TODO',
    payload: fetch(`/todos/${id}`)
  }
}

// Or 
const fetchTodo = (id) => {
  return fetch(`/todos/${id}`)
           .then(todo => {
               return {
               type: 'FETCH_TODO',
               payload: todo
             }         
           })
}

store.dispatch(fetchTodo(1))

[note] redux-promise 这个 middleweare 可以识别 payload 为 promise 的 action 或 全由 promise 组成的整个 action。 [/note]

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[magic data-transition="cover-circle"]

use redux-thunk to Call API

const fetchTodo = (id) => {
  return (dispatch, getState) => {
    fetch(`/todos/${id}`)
      .then(todo => {
        dispatch(createAction(FETCH_TODO)({ todo }))
      })
      .catch(error => {
        dispatch(createAction(FETCH_TODO)(error))
      })
  }
}

store.dispatch(fetchTodo(1))

[note] redux-thunk 也可处理 promise。 [/note]

=====

use redux-thunk to Conditional Dispatch

const addTodo = (text) => {
  return (dispatch, getState) => {
    if (getState().todos.length <= 3) {
        dispatch(createAction(FETCH_TODO)({ todo }))
    }
  }
}

[note] redux-thunk 还可用于按需调用。 [/note]

=====

Use redux-thunk to Dispatch Multiple Actions at Once

const fetchTodo = (id) => {
  return (dispatch, getState) => {
    dispatch(createAction(START_FETCH_TODO)({ todo }))

    fetch(`/todos/${id}`)
      .then(todo => {
        dispatch(createAction(FETCH_TODO_SUCCESS)({ todo }))
        // dispatch(createAction(TODO_RECIVED)({ todo }))
      })
      .catch(error => {
        dispatch(createAction(FETCH_TODO_FAIL)(error))
      })
  }
}

[note] redux-thunk 还可用于批量调用多个 action。显然 redux-thunk 的适用场景要比 redux-promise 要广。 [/note]

[/magic]

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[magic data-transition="cover-circle"]

Overuse redux-thunk

const updateTodo = (id, text) => {
  return (dispatch) => {
     return dispatch(createAction(UPDATE_TODO)({ id, text }))
  }
}

[note] 并非所有的 action 都要写成 thunk 形式。 [/note]

====

Overuse redux-thunk

const mapStateToProps = (state, ownProps) => ({})
const mapDispatchToProps = (dispatch, ownProps) => ({
  updateTodo: (id, text) => {
    return (dispatch) => {
      return dispatch(createAction(UPDATE_TODO)({ id, text }))
    }
  },
  addTodo: (text) => {
    return (dispatch) => {
      return dispatch(createAction(ADD_TODO)({ id: uuid.v4(), text }))
    }
  },
  toggleTodo: (id) => {
    return (dispatch) => {
      return dispatch(createAction(TOGGLE_TODO)({ id: uuid.v4(), text }))
    }  
  },                
})

@connect(mapStateToProps, mapDispatchToProps)

[note] 把上面的方法 inline 后，就显得更碍眼了。 [/note]

====

Overuse reason ?

• Not familiar with bindActionCreators
• Suppose will take over everything
• Copy & paste

====

react-redux will auto use bindActionCreators

const mapStateToProps = (state, ownProps) => ({})
const mapDispatchToProps = (dispatch, ownProps) => ({
  updateTodo: (id, text) => {
    return (dispatch) => {
      return dispatch(createAction(UPDATE_TODO)({ id, text }))
    }
  },
  addTodo: (text) => {
    return (dispatch) => {
      return dispatch(createAction(ADD_TODO)({ id: uuid.v4(), text }))
    }
  },
  toggleTodo: (id) => {
    return (dispatch) => {
      return dispatch(createAction(TOGGLE_TODO)({ id: uuid.v4(), text }))
    }  
  },                
})

• ↓

const mapStateToProps = (state, ownProps) => ({})
const mapDispatchToProps = {
  updateTodo: (id, text) => createAction(UPDATE_TODO)({ id, text }),
  addTodo: (text) => createAction(ADD_TODO)({ id: uuid.v4(), text }),
  toggleTodo: (id) => createAction(TOGGLE_TODO)({ id: uuid.v4(), text }),                
}

// will auto call bindActionCreators(mapDispatchToProps, dispatch)

@connect(mapStateToProps, mapDispatchToProps)

====

redux-thunk Source Code

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

    return next(action);
  };
}

const thunk = createThunkMiddleware();
thunk.withExtraArgument = createThunkMiddleware;

export default thunk;

====

Fix The Overuse of redux-thunk

const updateTodo = (id, text) => {
  return (dispatch) => {
     return createAction('UPDATE_TODO')({ id, text })
  }
}

• ↓

const updateTodo = (id, text) => createAction('UPDATE_TODO')({ id, text })

[/magic]

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Thank You & QA