200行代碼寫一個簡易的dva

時間 2019-11-05

標籤代碼一個簡易 dva 简体版

原文原文鏈接

在美團實習的時候，第一次接觸到dva這樣的react框架，回學校的時候，就想有機會本身實現一下這樣的框架，雖然本身水平有限，可是能夠試一試哈。目標是實現dva model的同步和異步 dispatch action。react

看看 dva 的構成redux

let counterModel = {
	 namespace: 'counter',
	 state: {
	    num: 0
	 }
	 
	 reducers: {
	     add(state, action){
	         return {
            		num: state.num + 1
            }	
	     }
	 }
	}
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對state的更新緩存

var app = new dva();
app.model(counterModel);
app.start();
app._store.dispatch({
	type: 'counter/add'
});
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上述就是 dva 對 state 的更新，經過dispatch {type: A / B} 其中 A 是指 model的 namespace, B 是指 model 中 reducers 具體的reducer方法。app

其中 dva 對異步的處理是用 redux-saga 處理的，由於做者並不熟悉redux-saga，拿 redux-thunk 代替了。框架

好，咱們開工了

第一步建立store異步

const createStore = (reducer, initialState) => {
  let currentReducer = reducer;
  let currentState = initialState;
  let listener = () => { };

  return {
      getState() {
          return currentState;
      },
      dispatch(action) {
          let {
              type
          } = action;
          currentState = currentReducer(currentState, action);
          listener();
          return action;
      },
      subscribe(newListener) {
          listener = newListener;
      }
  }
  } 
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store 主要是存儲數據，開放state更新接口。async

第二步引入中間件 applyMiddleware函數

const compose = (...funcs) => {
 if (funcs.length === 0) {
     return arg => arg
 }

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

 const last = funcs[funcs.length - 1]
 const rest = funcs.slice(0, -1)
 return (...args) => rest.reduceRight((composed, f) => f(composed), last(...args));
 }


 const applyMiddleware = (...middlewares) => {
     return (createStore) => (reducer, initialState, enhancer) => {
         var store = createStore(reducer, initialState, enhancer)
         var dispatch = store.dispatch;
         var chain = [];
         var middlewareAPI = {
             getState: store.getState,
             dispatch: (action) => store.dispatch(action)
         }
         chain = middlewares.map(middleware => middleware(middlewareAPI))
         dispatch = compose(...chain)(store.dispatch)
         return {
             ...store,
             dispatch
         }
     }
 }
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redux 中間件洋蔥模型，修改了dispatch 方法。學習

引入異步中間件redux-thunk和logger中間件測試

const logger = store => next => action => {
    console.log('prevState', store.getState());
    let result = next(action);
    console.log('nextState', store.getState());
    return result;
	};

	const thunk = ({
	    dispatch,
	    getState
	}) => next => action => {
	    if (typeof action === 'function') {
	        return action(dispatch, getState);
	    }
	    return next(action);
	}
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這裏引入 redux-thunk 作異步處理。

加入測試model

let counterModel = {

  namespace: 'counter',

  state: {
      num: 0
  },

  reducers: {
      add(state, action) {
          console.log('reducer add executed');
          return {
              num: state.num + 1
          }
      },
      asyncAdd(state, action) {
          console.log('reducer asyncAdd executed');
          return {
              num: state.num + 1
          }
      },
      test(state, action) {
          console.log('reducer test executed');
          return {
              state
          }
      }
  }
  };

  let userModel = {
  
  namespace: 'user',

  state: {
      name: 'xxxx'
  },


  reducers: {
      modify(state, {
          payload
      }) {
          console.log('reducer modify executed');
          let {
              name
          } = payload
          return {
              name
          }
      }
  }
  };
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對不一樣model下的reducer進行分發

const combineReducer = (reducers) => (state = {}, action) => {
  let {
      type
  } = action;
  let stateKey = type.split('/')[0];
  let reducer = type.split('/')[1];

  reducers.map((current) => {
      if (current.name === reducer) {
          state[stateKey] = current(state[stateKey], action);
      }
  });

  return state;
  }
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這裏由於 combineReducer 是 reducer的總入口，在這裏根據action 的 type 轉發到具體model下的reducer方法

dva 構造函數

class dva {
      constructor() {
          this._models = [];
          this._reducers = [];
          this._states = {};
      }
      model(model) {
          this._models.push(model);
      }
      start() {
          for (var i = 0; i < this._models.length; i++) {
              this._states[this._models[i].namespace] = {
                  ...this._models[i].state
              };
              Object.keys(this._models[i].reducers).map((key) => {
                  if (this._models[i].reducers.hasOwnProperty(key)) {
                      this._reducers.push(this._models[i].reducers[key]);
                  }
              })
  
          }
          var rootReducer = combineReducer(this._reducers);
          let createStoreWithMiddleware = applyMiddleware(thunk, logger)(createStore);
          this._store = createStoreWithMiddleware(rootReducer, this._states);
          this._store.subscribe(() => {
              console.log(this._store.getState());
          })
      }
  }
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dva 構造方法主要工做是緩存model，建立store。

測試數據

var app = new dva();
app.model(counterModel);
app.model(userModel);

app.start();
app._store.dispatch({
    type: 'counter/add'
});

app._store.dispatch({
    type: 'user/modify',
    payload: {
        name: 'shadow'
    }
})

app._store.dispatch((dispatch, getState) => {
    setTimeout(() => {
        dispatch({
            type: 'counter/asyncAdd'
        })
    }, 5000);
})
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