Async / await is not working (javascript / DynamoDB)

Question

I have a DynamoDB Put request wrapped into an async function.

 async function putter(param1, param2) {

        const paramsPut = {
            TableName: MyTableName,
            Item: {
                "hashKey": param1,
                "sortKey": param2,
            }
        };

        dynamodb.put(paramsPut, function(err, data) {

            if (err) {
                console.log("Failure")
                console.log(data)
                return data
            }
            else {
                console.log("Success")
                console.log(data)
                return data
            }
        });
    };

The return for the async funtion is placed in the response function - this the should provide back a promise upon put operation was performed (either sucessfully or not sucessfully).

I then invoke this async put function from another async function:

    var param1 = "50";
    var param2 = "60";


    async function main() {

        await putter(param1 , param2)
        console.log("Feedback received")

    }

When I invoke this aysnc main function I would expect it to provide the Success statement from the put function prior to writing "Feedback received" as it should await the put function response.

However my console logs the "Feedback received" prior to logging the "Success" statement in the put async function which I was awaiting.

What am I missing here? Thanks for your support!

Can please share complete code after modification(Working Code) — Komal Cr
– Komal Cr, Commented Jan 7, 2021 at 10:46

ttulka · Accepted Answer · 2019-05-05 15:37:44Z

50

Try to change your code like follows:

try {
    const data = await dynamodb.put(paramsPut).promise()
    console.log("Success")
    console.log(data)
    return data
} catch (err) {
    console.log("Failure", err.message)
    // there is no data here, you can return undefined or similar
}

Almost every function from AWS SDK has the promise() variant to return the result as a Promise. Then you can just await the Promise. Don't mix callbacks with promises (async/await) - it makes the code hard to read, it's better to stick with one technique everywhere.

edited May 5, 2019 at 15:37

answered May 5, 2019 at 15:26

ttulka

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6 Comments

Geole Over a year ago

Dear Tomas, that worked perfectly! Thank you so much. Do you have any idea, why the previous code did not work? I was expecting the "return" in the async function to return a promise when placed into the function called after put-completion...

ttulka Over a year ago

Your problem was that calling return in a callback function has no effect at all, because the callback is in fact an anonymous function and no one is interested in its return value, so it will be ignored and the wrapping function ends up always returning nothing. Happy to help, you can accept the answer then.

Xin Over a year ago

Nice one it helped. BTW, what is the difference put and putItem I only saw putItem?

ttulka Over a year ago

@Xin Those are different APIs: DynamoDB::putItem vs DynamoDB.DocumentClient::put.

Xin Over a year ago

@ttulka Thank you. DOcumentClient is more well interface frendly, easier to use. thanks.

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