AWS DynamoDB JavaScript SDK 的返回值未定义

Question

I am currently using the JavaScript AWS SDK for DynamoDB and I am trying to parse the data I get from a DynamoDB call, but it always returns undefined. It does print the result successfully, but trying to store that data in a variable is unsuccessful. Below is how I am attempting to do it.

const AWS = require("aws-sdk");
AWS.config.update({ region: "us-east-1" });
const dynamoDb = new AWS.DynamoDB({ apiVersion: "2012-08-10" });

const promisify = foo =>
  new Promise((resolve, reject) => {
    foo((error, result) => {
      if (error) {
        reject(error);
      } else {
        resolve(result);
      }
    });
  });

const params2 = {
  TableName: "Users",
  Key: {
    userID: { S: "123456789" },
  },
};

const test = params => {
  dynamoDb.getItem(params, function(err, data) {
    if (err) {
      console.log("Error", err);
    } else {
      console.log("Success", data.Item);
      return data.Item;
    }
  });
};

let user = test(params2);
console.log("User:", user);

I believe it has to do with getItem being asynchronous and I have researched how to implement a promise into this code, but I cannot get the correct syntax. Any and all help is greatly appreciated. Thank you.

Answer 1

The problem you have is that you are not returning anything from your test function. So it is expected that you get undefined outside.

Try to do it like this:

// used aws promise api https://docs.aws.amazon.com/sdk-for-javascript/v2/developer-guide/using-promises.html
function test(params) {
    return dynamoDb.getItem(params).promise();
}

test(params2).then(
    user => {
        console.log('User:', user);
    },
    error => {
        console.log('Error:', error);
    },
);

Some further read:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function