正確處理承諾拒絕

Question

考慮以下代碼：

db.js

// Connecting to catalogstore (mongodb)
const mydb = async () => {
  try {
    await mongoose.connect(process.env.db);
    console.log("Connected to Database!");
  }
  catch (err) {
    throw new Error("Database connection error:", err);
  }
};

export { db }

app.js

import { db } from './db';
db().then(async() => {
  try {
    let server = app.listen(process.env.port,
      process.env.host, function() {
        let host = server.address().address;
        let port = server.address().port;
        console.log('App started');
    });
  } catch (err) {
    console.log(err);
  }
});

基本上，我只想在建立數據庫連接后啟動Express服務器。

它實際上工作正常，但是我收到此警告：

(node:29892) UnhandledPromiseRejectionWarning: Error: Database connection error:
    at catalogstore (/Users/notaris/Workspace/Google/gcp-devops/apps/catalogservice/src/db.js:44:11)
    at processTicksAndRejections (internal/process/task_queues.js:89:5)
(node:29892) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:29892) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

我該如何正確處理？

Answer 1

該錯誤由db async函數引發。

處理此Error的正確方法（使用異步函數/箭頭）是：

import { db } from './db';
const main = async () => {
  try {
    await db();
    let server = app.listen(process.env.port,
      process.env.host, function() {
        let host = server.address().address;
        let port = server.address().port;
        console.log('App started');
    });
  } catch (err) {
    console.log(err);
  }
});
main();

Answer 2

修改app.js，如下所示

import { db } from './db';
db()
  .then(/* normal logic */)
  .catch(/* error logic */)

趕上它^^

Answer 3

在調試器中，我看到您應該在promise中捕獲錯誤，如下所示：

//app.js
import { db } from './db';
db().then(async() => {
  try {
    let server = app.listen(process.env.port,
      process.env.host, function() {
        let host = server.address().address;
        let port = server.address().port;
        console.log('App started');
    });
  } catch (err) {
    console.log(err);
  }
}).catch(error=>{
     console.log('error'+error);
});

您可以檢查此鏈接以獲取更多詳細信息。