Promise is pending

Question

I have a class in my nodejs application with the following code:

var mongoose    = require('mongoose');
var Roles       = mongoose.model('roles');
var Promise     = require("bluebird");

module.exports = Role;

var err = null;
var id;

function Role(name, companyId) {
    this.err = err;
    this.name = name;
    this.companyId = companyId;
    this.id = getId(name, companyId);
}



var getId = function (name, companyId) {
     return new Promise(function(resolve, reject) {
        Roles.findOne({companyId:companyId, name:name}, function(err,result) {
              resolve(result._id);
        });
     });
};

When I am calling the class, the id is pending:

var currentRole = new Role(myRole, comId);
console.log(currentRole);

How can I get the values from the class when they are resolved?

Have a look at [Is it bad practice to have a constructor function return a Promise?](http://stackoverflow.com/q/24398699/1048572) - you probably don't want to do `currentRole.id.then(…)` — Bergi, Apr 24 '16 at 10:53

Matt Harrison · Accepted Answer · 2016-04-24T10:59:17.030

currentRole.id is a promise so you can call then() on it to wait for it to be resolved:

var currentRole = new Role(myRole, comId);
currentRole.id.then(function (result) {

    // do something with result
});

This feels like a strange API though, you expect your object to be "ready to use" when its constructor returns. Might be better to have getId be a promise returning function on the prototype of Role so you instead do something like:

var currentRole = new Role(myRole, comId);
currentRole.getId().then(function (result) {

    // do something with result
});

You should also consider handling that error to reject the promise:

var getId = function (name, companyId) {
     return new Promise(function(resolve, reject) {
        Roles.findOne({companyId:companyId, name:name}, function(err,result) {

              if (err) {
                  return reject(err);
              }
              resolve(result._id);
        });
     });
};

and add a rejection handler to your call to getId:

var currentRole = new Role(myRole, comId);
currentRole.getId().then(function (result) {

    // do something with result
}, function (err) {

    // do something with err
});

or equivalently:

var currentRole = new Role(myRole, comId);
currentRole.getId().then(function (result) {

    // do something with result
}).catch(function (err) {

    // do something with err
});

Thank you Matt! I used your last suggestion, and the code works now and looks much cleaner. — Danish Woman, Apr 25 '16 at 04:35

Promise is pending

1 Answers1