Node.js Callback to Promise Promisifying a callback


Example

Callback-based:

db.notification.email.find({subject: 'promisify callback'}, (error, result) => {
   if (error) {
       console.log(error);
   }

   // normal code here
});

This uses bluebird's promisifyAll method to promisify what is conventionally callback-based code like above. bluebird will make a promise version of all the methods in the object, those promise-based methods names has Async appended to them:

let email = bluebird.promisifyAll(db.notification.email);

email.findAsync({subject: 'promisify callback'}).then(result => {

    // normal code here
})
.catch(console.error);

If only specific methods need to be promisified, just use its promisify:

let find = bluebird.promisify(db.notification.email.find);

find({locationId: 168}).then(result => {
    
    // normal code here
});
.catch(console.error);

There are some libraries (e.g., MassiveJS) that can't be promisified if the immediate object of the method is not passed on second parameter. In that case, just pass the immediate object of the method that need to be promisified on second parameter and enclosed it in context property.

let find = bluebird.promisify(db.notification.email.find, { context: db.notification.email });

find({locationId: 168}).then(result => {

    // normal code here
});
.catch(console.error);