How to return AWS IAM user as a string/json using STS GetCallerIdentity Caller JS/TS

Question

I'm trying to get AWS IAM Arn user using STS GetCallerIdentity API Amazon provided. The code below basically logs the correct data in the console. However, i want to return the data as a string/json and I can't seem to return the value because it's inside a parameter.

How can I return the information I need that's in the data callback?

Any tips/advice would be very much appreciated!!

export function GetIamUser() {
    const sts = new AWS.STS();

    sts.getCallerIdentity({}, function (err, data) {
        if (err) console.log(err, err.stack);
        else console.log(data);
    });
}

https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/STS.html#getCallerIdentity-property

This is the output when I run the method above

   data = {
    Account: "123456789012", 
    Arn: "arn:aws:iam::123456789012:user/user", 
    UserId: "AKIAI44QH8DHBEXAMPLE"
   }

UPDATE: I've tried returning the function callback by the method below, however the value keeps returning undefined

export function GetArnUser() {
    var user;
    sts.getCallerIdentity({}, function (err, data) {
        if (err) console.log(err, err.stack);
        else console.log(data);
        user = data.Arn;
    });
    return user;
}

Answer 1

This is an async issue. you are using callbacks, which means you need to pass a callback function to GetArnUser(), similar to the below

export function GetArnUser(cb) {
    var user;
    sts.getCallerIdentity({}, function (err, data) {
        if (err) console.log(err, err.stack);
        else {
            console.log(data);
            user = data.Arn;
            cb(user)
        }
    });
}