Question

reducers.reduce(
  (p, r) => r(p, current),
  previous,
);

Reducer是一个函数数组r(p, current)将返回一个对象。我试图从这里https://github.com/dvajs/dva/blob/master/packages/dva-core/src/handleActions.js了解源代码，但有点混淆这个陈述。什么减少到？

我试图使用reduce函数，它似乎只是取最后一个值（如果我不像这种情况那样转换值）？

var array1 = [0, 1, 2, 3];
const result = array1.reduce((accumulator, currentValue) => currentValue);
console.log(result);

Answer 1

当您查看整个功能而不是您引用的部分时，它会更容易理解：

function reduceReducers(...reducers) {
  return (previous, current) =>
    reducers.reduce(
      (p, r) => r(p, current),
      previous,
    );
}

......以及调用该函数时会发生什么：

const reducer = reduceReducers(...reducers);

reduceReducers(...reducers)返回函数，当使用reducer(state, action)调用时，将状态作为初始值/数组并传递用作累加器p 。 action传递为current，因此调用reducer r可能会根据操作创建新状态。

让我们再看看，这次注释：

// `reduceReducer` takes an array of reducers
function reduceReducers(...reducers) {

  // It returns a new function that accepts 2 arguments:
  // `previous` and `current`
  // This function is assigned to the variable `reducer`
  return (previous, current) =>

    // `reducers` can still be called here because of
    // the closure that formed - the returned function
    // maintains its outer lexical environment
    reducers.reduce(

      // On each iteration the accumulator is passed in.
      // In the initial iteration this is the value of `state`
      // On each iteration the value of the next reducer called with
      // the new state and the action is returned
      (p, r) => r(p, current),

      // `previous` is passed in as the initial value
      // When `reducer` is called `reducer(state, action)`
      // this means that `state` is `previous`
      previous,
    );
}

希望这更清楚一点。

什么是减少使用当你没有积累任何东西

1 个答案: