How to get data from inside a response function in Nods js

Question

Im a new user of Nodejs and Javascript

I have this class :

class Users {
    constructor() {
        this.all;
        this.selectAll();
    }
    async selectAll() {
      await connection.connect(() =>
            connection.query(`SELECT * FROM users`, (err, result) => {
                this.setData(result);
            }),
        );
    }

    setData(res) {
        this.all = res;
    }
}

I want to get result of data from the response function selectAll(); for example:

var db = new Users();
console.log(db.all);

I expected db.all to give me result of selectAll()

Is there any better idea?

You need to use `await`, you are trying to access property before the response is received. — Leau, Dec 26 '21 at 21:17
You need to await `this.selectAll` call and at your instance creation too. — Leau, Dec 26 '21 at 21:26
But it's really hacky, I suggest you to use an alternative way. — Leau, Dec 26 '21 at 21:27
Take a look at here https://stackoverflow.com/a/50885340/14346900. — Leau, Dec 26 '21 at 21:28
@Leau please let me know any better way for this issue. thanks — Rai Rz, Dec 26 '21 at 21:28
@Leau I'm a new user of the node and javascript. could you please answer this question with your idea? thanks — Rai Rz, Dec 26 '21 at 21:33
I begin wonder what the point of that entire class is. The ability to access the "return value" (`all`) independent of the function that creates / "returns" the value (`selectAll`) seems just like a source for errors. So why not make this a plain old function. assuming that `const connection = require("mssql")` how about `export async function selectAll() { await connection.connect(); return connection.query\`SELECT * FROM users\`; }` — Thomas, Dec 26 '21 at 22:32

Steve · Answer 1 · 2021-12-26T21:42:57.240

1

You want to await this.selectAll seeing as it is a promise. So you need to make sure it returns a promise. You could make the constructor async to await the selectAll but this is not advised and probably won't work.

Personally, I would just call db.selectAll after creating the instance of users.

Maybe something like this:

File: Users.js

export class Users {
    all = null

    async selectAll() {
        return connection.connect(() =>
            connection.query(`SELECT * FROM users`, (err, result) => {
                this.setData(result);
            })
        );
    }

    setData(res) {
        this.all = res;
    }
}

File: index.js (or anywhere else)

import { Users } from './Users.js'

// Somewhere else in your code in an async function:
const anotherPlace = async () => {
    const db = new Users();
    await db.selectAll();
    console.log(db.all)
}

edited Dec 26 '21 at 21:42

answered Dec 26 '21 at 21:32

Steve

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Thanks. but I want to get response data from outside of class easily. I want do it inside the class – Rai Rz Dec 26 '21 at 21:40
I understand you want minimal code outside of the class but its a dangerous practice to use async await in a constructor so for the sake of good practices you really should just call that one extra line outside of the class to populate `all`. – Steve Dec 26 '21 at 21:46
2

@MikelWilliams Well you could make it that `await db.selectAll()` also returns the value; saves a few characters, but it's either this here or making `db.all` itself a Promise. You need to deal outside of `User` with the fact that your DB-request takes time to fulfil and the result ain't available immediately and you have no clue when the value will be available. Except for the Promise. – Thomas Dec 26 '21 at 22:03
In that case, you could possibly look into an async getter https://stackoverflow.com/a/39387979/5553768 but that is pretty horrible. I think there is such thing as over-simplifying which ends up making things more difficult in the long run. – Steve Dec 26 '21 at 22:10
@Steve I'm using the User Class coz I want to make a code shorter as much as possible. your solution has been used with a long code. If should use an ugly and long code so why developer uses a class ever?!?! – Rai Rz Dec 26 '21 at 22:48
1

Not sure what to tell you mate, this is much nicer than the alternative. Maybe start here to understand how classes benefit us: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes – Steve Dec 26 '21 at 23:04

How to get data from inside a response function in Nods js

1 Answers1