How to get a variable value outside a callback function NodeJS

Question

I'm trying to get the value of an inputed variable on a callback function and assign it into another variable value outside this callback function. I'm using async/await but not working (the assignment runs before the callback function), any suggestion?

async function iniciar() {
    let my_prep = '';
    await readline.question('Insert preposition', (prep) => {
      **my_prep = prep;**
      readline.close();
    });
    console.log('OK',my_prep);
    return true;
}

Thanks for reading!

await keyword waits on promise does your function readline.question returns a promise? — alt255
– alt255, Commented Nov 28, 2020 at 12:15
Readline's question() function does not return Promise or result of the arrow function. So, cannot use then() with it. @alt255 — arevilla009
– arevilla009, Commented Nov 28, 2020 at 12:24

alt255 · Accepted Answer · 2020-11-28 12:22:00Z

4

You can do something like this.

const question = () => {
  return new Promise((resolve, reject) => {
    readline.question('Insert preposition ', (prep) => {
      readline.close();
      resolve(prep)
    })
  })
}



async function iniciar() {
  let my_prep = await question();
  console.log('OK',my_prep);
  return true;
}

await keyword waits on the promise to resolve, so you need to return promise. Also the use of async/await and promises is to avoid callback hell.

answered Nov 28, 2020 at 12:22

alt255

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1 Comment

arevilla009 Over a year ago

Exactly want I needed! Thanks for the reply! @alt255

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