是否可以将参数传递给使用let初始化的变量

Question

下面是我正在学习的一个教程中使用的代码片段。有人能帮助理解如何将参数"mediastate"传递给"notify"函数中的变量"transientListen"吗？

function createMediaListener(queries) {
let transientListener = null;
const keys = Object.keys(queries);
const queryLists = keys.reduce((queryLists, key) => {
queryLists[key] = window.matchMedia(queries[key]);
return queryLists;
}, {});
const mediaState = keys.reduce((state, key) => {
state[key] = queryLists[key].matches;
return state;
}, {});
const notify = () => {
if (transientListener != null) transientListener(mediaState);
};
const listeners = keys.reduce((listeners, key) => {
listeners[key] = event => {
mediaState[key] = event.matches;
notify();
};
return listeners;
}, {});
const listen = listener => {
transientListener = listener;
keys.forEach(key => {
queryLists[key].addListener(listeners[key]);
});
};
const dispose = () => {
transientListener = null;
keys.forEach(key => {
queryLists[key].removeListener(listeners[key]);
});
};
const getState = () => mediaState;
return { listen, dispose, getState };
}
export default createMediaListener;

Answer 1

我如何理解；听"；函数由模块中的return语句调用。问题是；听"；函数需要一个参数，否则为：transientListener=listener=>未定义。