强制程序执行，直到功能完成

Question

I am trying to make a connection to a database and would like to see that my code stops executing while the connection has not been established yet. So it can print an error/success message to the console at the right time (before the program will output that startup was successful).

My current code to establish the connection is:

dbConnectAsync = async () => {
  try {
    await mongoose.connect("mongodb://localhost:27017/meetstation", { useNewUrlParser: true });
    console.log(SUCCESS_MSG);
  } catch (err) {
    console.log(ERROR_MSG);
    console.log(err.name);
  }
}

I know it is possible to put all other code inside the try block but this is not desirable as I plan on moving the function that establishes the database connection to an other file.

Is there any way to call this function that forces other execution of code to wait until this function is done executing?

Answer 1

Within your code you can await dbConnectAsync and then run after the successful connection occurs. So code will appear in a separate try/catch block, but not in the internal try/catch of dbConnectAsync .

async function program() {
    try {
        await dbConnectAsync();
        // code that executes after successful connection
    } catch (err) {
        // handle connection error
    }
}

One change I would mention is to use throw in the catch block of dbConnectAsync so that any consuming code can respond to it. My example above won't receive any errors as a result.

Answer 2

You could extract the database setup function into module:

// db.js
let connection;

export async function setup() {
  try {
    connection = await mongoose.connect('mongodb://localhost:27017/meetstation', { useNewUrlParser: true });
    console.log(SUCCESS_MSG);
  } catch (err) {
    console.log(ERROR_MSG);
    console.log(err.name);
  }
}

export function getConnection() {
  return connection;
}

Init the connection and then start your application:

// main.js
import { setup, getConnection } from './db.js';

(async function bootstrap() {
  await setup();

  // start your application
  // using getConnection()
})();

Answer 3

Actually your server can't do much without a database. Therefore the most appropriate reaction in case of an error is just to crash. With top-level await I would just write a module like this:

  export * from "mongoose";
  import { connect } from "mongoose";

  await connect("mongodb://localhost:27017/meetstation", { useNewUrlParser: true });

Then whenever you use mongoose, import it from that file and not from "mongoose" itself. That way, no code will run until the database is ready and in case of an error the server does crash.