AWS s3.listBuckets save data object in global variable - nodejs

Question

I am trying to read the buckets in an account and save the list to a variable that can be accessed by other functions.

I am trying using a global variable.

Result: Global variable value not retained/saved.

Node: v10 Code:

var AWS = require('aws-sdk');
AWS.config.update({region: 'eu-west-1'});

s3 = new AWS.S3({apiVersion: '2006-03-01'});
let blist;
getBuckets();
console.log("list: " + blist);

async function getBuckets() {
     let response = await s3.listBuckets().promise();
      // do your processing
      var buckets = response.Buckets.map(x=>x.Name);
      console.log("buckets: " + buckets);
      blist = buckets;
      //return bnames;
}

Output:

Output:

(GV) List: undefined  (blist) 
(LV) Buckets: [all good]

Global variable value is undefined.

Can someone please help me? All I need is to access the list of bucket names from a different function.

s3.listBuckets() does't return text, it returns a request object... which you don't need when invoking it asynchronously, as you are doing. docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/… Your return ndata; in the callback doesn't make sense, because the turn value from callbacks is discarded. — Michael - sqlbot
– Michael - sqlbot, Commented Jun 10, 2018 at 16:18

Dilip Kola · Accepted Answer · 2018-06-10 16:59:45Z

2

s3.listBuckets is an asynchronous function so when you assign to a variable you won't get expected result. you better consider using promises to chain them or use async/await.

Using promises:

s3.listBuckets().promise()
       .then((response) => {
          // do your processing
        });

Using async/await:

async function someFn() {
     let response = await s3.listBuckets().promise();
      // do your processing
}

answered Jun 10, 2018 at 16:59

Dilip Kola

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1 Comment

AHM Over a year ago

Thank you, @dilip for the explanation. I tried using the async function and it is still the same. I have now modified the initial post with the updated program. blist global variable is still undefined, but buckets local variable gets all the bucket names.

BigMan73 · Accepted Answer · 2021-06-10 16:01:48Z

0

This minimal code works:

import S3 from "aws-sdk/clients/s3.js";

const main = async () => {
  const s3 = new S3({ apiVersion: "2006-03-01" });

  const buckets = await s3.listBuckets().promise();
  console.log(JSON.stringify(buckets));
};

(async () => {
  try {
    await main();
  } catch (e) {
    console.error(e);
  }
})();

answered Jun 10, 2021 at 16:01

BigMan73

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