ways to retrieve the value from a promise

Question

ways to retrieve the value from a promise

I have a function to find the MX records of a service and I want to save the value with the lowest priority in order to make a request to it. How can I store and retrieve this value?

const dns = require('dns');
const email = '<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="c8e6e6e688afa5a9a1a4e6aba7a5">[email protected]</a>'
let res = email.split('@').pop();

function getMxRecords(domain) {
  return new Promise(function(resolve, reject) {
    dns.resolveMx(domain, function(err, addresses) {
      if (err) {
        //console.log(err, err.stack)
        resolve(null);
      } else {
        //console.log(addresses);
        let copy = [...addresses];
        //console.log(copy);
        let theone = copy.reduce((previous, current) => {
          if (previous.priority < current.priority) {
            return current;
          }
          return previous;
        });
        resolve(theone);
      }
    });
  });
}

let a = getMxRecords(res);
console.log(a);

I need to export this module so that I can make a request to it as shown below;

let socket = net.createConnection(25, request(email), () => {})

When attempting to use my function, I expect to receive either a string or an object with only one value. However, I always encounter the following issue:

Promise { }

Error in socket connect ECONNREFUSED 127.0.0.1:25

javascript dns

Answer 1

Answer №1

A Promise represents an asynchronous operation that will either be resolved or rejected. To access the outcome, certain functions need to be called:

function fetchUserData(username) {
  return new Promise(function(resolve, reject) {
    api.getUserData(username, function(err, data) {
      if (err) {
        //console.log(err, err.stack)
        resolve(null);
      } else {
        //console.log(data);
        let user = { ...data };
        //console.log(user);
        resolve(user);
      }
    });
  });
}

fetchUserData(username)
  .then(userData => {
    // Code to handle successful promise resolution
  })
  .catch(error => {
    // Code to handle promise rejection. 'error' parameter contains provided error details.
  })

Answer 2

A Promise represents an asynchronous operation that will either be resolved or rejected. To access the outcome, certain functions need to be called:

function fetchUserData(username) {
  return new Promise(function(resolve, reject) {
    api.getUserData(username, function(err, data) {
      if (err) {
        //console.log(err, err.stack)
        resolve(null);
      } else {
        //console.log(data);
        let user = { ...data };
        //console.log(user);
        resolve(user);
      }
    });
  });
}

fetchUserData(username)
  .then(userData => {
    // Code to handle successful promise resolution
  })
  .catch(error => {
    // Code to handle promise rejection. 'error' parameter contains provided error details.
  })

ways to retrieve the value from a promise

Answer №1

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