AWS Javascript SDK with Promises

Question

I am trying to use AWS Javascript SDK for accessing S3. I am using the Promises with 'Q' library. However it is not working. I have set the Q dependency also.

var Q = require('q');
AWS.config.setPromisesDependency(Q);

Here's the code I have:

var listBucketPromise = s3.listBuckets().promise();
listBucketPromise.then(
    function (response) {
        console.log(" response = " + response );
    } ,
    function (error) {
        console.log(" error = " + error);
    }
);

This shows on console :

response = function (resolve, reject) {
      self.on('complete', function(resp) {
        if (resp.error) {
          reject(resp.error);
        } else {
          // define $response property so that it is not enumberable
          // this prevents circular reference errors when stringifying the JSON object
          resolve(Object.defineProperty(
            resp.data || {},
            '$response',
            {value: resp}
          ));
        }
      });
      self.runTo();
    }

I have a valid s3 client set correctly. The callback format works:

s3.listBuckets(function (err, data) {
    console.log(data);
});

Why is the promise code not working ?

What do you mean by "This shows on console", is that an error message? — Bergi
– Bergi, Commented Jun 11, 2017 at 12:13
Assuming that setPromisesDependency expects a promise constructor, try passing Q.Promise instead — Bergi
– Bergi, Commented Jun 11, 2017 at 12:14
I am testing the script via WebStorm terminal. That's what I meant by console. The code that prints that log is : console.log(" response = " + response ); — Manish
– Manish, Commented Jun 11, 2017 at 12:34
AWS.config.setPromisesDependency(Q.Promise); did make the difference.. I am able to get the response now.. Many thanks !. If you could post that as an answer, I will be happy to accept it.. :) — Manish
– Manish, Commented Jun 11, 2017 at 12:40

Bergi · Accepted Answer · 2017-06-11 12:44:47Z

1

You need to pass a Promise constructor to setPromisesDependency. The Q function that you used does not expect a callback, when called with the typical promise executor callback it just returned a promise fulfilled with that function value.

You can use Q.Promise instead, which also is documented in this blog post's example:

// Use Q implementation of Promise
AWS.config.setPromisesDependency(require('Q').Promise);

answered Jun 11, 2017 at 12:44

Bergi

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