How to await in constructor?

Question

I try to use await in class constructor but failed, here are my trys:

export class TheHistory {
  constructor(private readonly db: EntityManager){
        //try1: too many levels !!! try use await
        mydb.insert(god).then(() => {
          mydb.insert(human).then(() => {
            mydb.insert(city).then(() => {
              //.....
            })
          })
        })

        //try2: ERROR -- 'await'expressions are only allowed within async functions and at the top levels of modules
        await mydb.insert(god)
        await mydb.insert(human)
        await mydb.insert(city)
  }
}

Create a new async method, move your code to that, and then call that method from your constructor. — Andy, Aug 10 '21 at 03:53
https://stackoverflow.com/a/50885340/9418800 I think this is what you need — moshfiqrony, Aug 10 '21 at 04:00
You shouldn't do anything asynchronous in your constructor, because you can't handle errors. — Evert, Aug 10 '21 at 04:39

kyun · Answer 1 · 2021-08-10T05:18:58.837

0

export class TheHistory {
  constructor(private readonly db: EntityManager){
    this.init(db);
  }
  async init(mydb){
    await mydb.insert(god)
    await mydb.insert(human)
    await mydb.insert(city)
  }
}

maybe you can do like this.

edited Aug 10 '21 at 05:18

answered Aug 10 '21 at 03:56

kyun

8,693
8
27
56

1

this.init(db) inside constructor – Bipin Shrestha Aug 10 '21 at 04:02
1

I think this is an anti-pattern in many cases because the constructor will return immediately, which could be leaving the object in an invalid state for some other code to use. I'd instead use a static function that awaits all the necessary values and returns `Promise`. – Mack Aug 10 '21 at 05:31

score 0 · Answer 2 · answered Aug 10 '21 at 03:59

You can only use await inside an async function, so either extract the code to an async method or use a immediately-invoked async function expression.

constructor(private readonly db: EntityManager){
    (async()=>{
        await mydb.insert(god)
        await mydb.insert(human)
        await mydb.insert(city)
    })();
}

score -1 · Answer 3 · answered Aug 10 '21 at 03:56

-1

Try call to constructor from outside

async function foo () {
    var myObj = await mydb.insert(god);
}

answered Aug 10 '21 at 03:56

Dilan Fernando

1
1

How to await in constructor?

3 Answers3