javascript - ReactJS中的提升函数

Question

const updateSearchTopStoriesState = (hits, page) => (prevState) => {
const { searchKey, results } = prevState

谁能给我解释一下上面的作用是什么？为什么有2个箭头函数？

这是完整的代码

const updateSearchTopStoriesState = (hits, page) => (prevState) => {
const { searchKey, results } = prevState;
const oldHits = results && results[searchKey]
? results[searchKey].hits
: [];
const updatedHits = [
...oldHits,
...hits
];
return {
results: {
...results,
[searchKey]: { hits: updatedHits, page }
},
isLoading: false
};
};
class App extends Component {
...

Answer 1

连续的两个箭头函数称为 thunk。

简单来说，这种格式更容易理解:

function updateSearchTopStoriesState = (hits, page) {
   function updateState (prevState) {
    ...code
   }
   return updateState;
}