loopback async/await UnhandledPromiseRejectionWarning issue

[dyaa]

In loopback 3 When i implement async/await in the before save Operation hook

Entry.observe('before save', async (ctx, next) =>{

    if(ctx.instance.images){
        Entry.upload(ctx.instance.images[0].src).then(data => {
            ctx.instance.image = data;
        });
    }
});

the console print this error

(node:29323) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): Error: Callback was already called.
(node:29323) DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

How can i get rid of this issue!?

PS. i cant figure out where's that promise, and this message disappear once i remove the async/await.

[MohammedEssehemy]

I think your code should be restructured like that:

       Entry.observe('before save', async (ctx, next) =>{
           if(ctx.instance.images){
              let data = await(Entry.upload(ctx.instance.images[0].src));
              ctx.instance.image = data;
                    }
               });

if your code async code throw error it will be passed to next automatically

[yqrashawn]

loopback3 already support async function.

Entry.findFooById = async (id, cb) => {
  const result = await Entry.findById(id);
  return result;
};

Entry.findFooById = (id, cb) => {
  Entry.findById(id)
    .then(result => cb(null, result))
    .catch(cb);
};

These two functions will accomplish the same functionality.

[dmastag]

@yqrashawn
Thanks but am curious how would you return multiple returns using that way?

For instance, if we have this code

module.exports = function(Person){

    Person.greet = function(msg, cb) {
      cb(null, 'Greetings... ' + msg, 'Greeting2 Message');
    }

    Person.remoteMethod('greet', {
          accepts: {arg: 'msg', type: 'string'},
          returns: [
             {arg: 'greeting', type: 'string'},
             {arg: 'greeting2', type: 'string'}
         ]
    });
};

How can I use async await and return 2 values?

[dmastag]

Nevermind, I found out how to do it by trying multiple options

You can replace

cb(null, 'Greetings... ' + msg, 'Greeting2 Message');

into

return ['Greetings... ' + msg, 'Greeting2 Message'];