为什么我们使用（）=> []而不是[]？

Question

i have a short question about a reducer in React Native

Why do I have to write the code like this:

import { combineReducers } from 'redux';

export default combineReducers({
    reducerKey : () => []
});

instead of this:

import { combineReducers } from 'redux';

export default combineReducers({
    reducerKey : []
});

Basically: Why does it have to be a function? Thanks!

Answer 1

The job of the reducer is to apply some input to update the state. The reducer returns the new state after an action is performed. It works on an input and may return a different state on different input, hence it is a function.

If you use the second approach, you generate a fixed value of state, which could be valid for some use cases. But generally, you'd want to use a function.

Answer 2

First, you need to know what are they?

() => [] is an arrow function which returns an empty array but [] is just an empty array.

---

See the doc's note :

reducers (Object): An object whose values correspond to different reducing functions that need to be combined into one.

So, you'll need to pass a function in reducer. So you'll use () => [] instead of [] .

---

I have never used such with combineReducers. This is used to combine the different reducers like:

combineReducers({
  reducer1,
  reducer2
})

The preceding example is just an alias of:

combineReducers({
  reducer1: reducer1,
  reducer2: reducer2
})