分解函数参数中的默认值导致ReferenceError

I needed to set a default value for db in my CRUD functions for testing purposes and encountered a strange behaviour, I could not figure out yet. Consider the following code:

import { db } from './firebase'

function getUsers({ db = db }) {
  try {
    return db
    ...

Now, when I use the function in my tests, there is no problem, since I invoke the function in my test file with a test db. But the real app should be able to fall back on the default value and call the function without any params. But here, I encounter the error: ReferenceError: can't access lexical declaration 'db' before initialization. I have no idea why this happens.

我通过重命名参数找到了解决方法。但是，我仍然很想知道这里发生了什么。有人有主意吗？

解决方法：

import * as firebase from './firebase'

function getUsers({ db = firebase.db }) {
  try {
    return db