DAPP development using MetaMask API in Vue is invalid

DAPP development using MetaMask API in Vue is invalid
Vue version 3.2.25
MetaMask version 10.8.1
Chromium version 90.0.4430.93 (official version) (64-bit)
Use mounted to get

mounted() {
console.log(window.ethereum.selectedAddress);
},

The result is:

0x348f....

But after using npm run bulid

null

further testing

mounted() {
console.log(typeof window.ethereum);
console.log(window.ethereum);
console.log(window.ethereum.selectedAddress)
},

object
Proxy {_events: {…}, _eventsCount: 1, _maxListeners: 100, _log: u, _state: {…}, …}
null

But there is no such problem in the browser console

ethereum
Proxy {_events: {…}, _eventsCount: 1, _maxListeners: 100, _log: u, _state: {…}, …}
ethereum.selectedAddress
"0x348fd452409cf4dd75027394394bef9ec2f09213"

The guess is that it takes a certain amount of time for MetaMask to obtain selectedAddress, and there is a problem with the order of execution. However, the Vue life cycle seems to have hooks before Mounted and after mounted.
Final solution Promise:

mounted() {
console.log(typeof window.ethereum);
console.log(window.ethereum);
//Asynchronously implement browser MetaMask API post-loading issues
this.sleep(500).then(() => {
// console.log(window.ethereum.selectedAddress);
})
},
methods: {
//Asynchronously implement browser MetaMask API post-loading issues
sleep(time) {
return new Promise((resolve) => setTimeout(resolve, time));
}
}

As for why there is no such problem in dev:
dev

30 requests
10.2 MB transferred
10.2 MB resources
Finish: 896 ms
DOMContentLoaded: 800 ms
Load: 907 ms

build

0 requests
2.0 MB transferred
2.0 MB resources
Finish: 813 ms
DOMContentLoaded: 295 ms
Load: 420 ms

Perhaps too many dependencies under dev just give metamask enough time to take effect.
In other words, if there are enough dependencies after build or the metamask is fast enough, after the website is online and the network delay is added, will this problem disappear? . .