Returning asynchronous data then exporting it synchronously in Node.js

Question

Background

I am returning data from AWS Secrets Manager and using the aws-sdk to do so. Earlier I asked a question about how to correct

Answer 1

I would suggest doing everything in 1 file, and then instead of exporting the object you create, export a function that returns the object. The function will always have access to the must up-to-date version of the object, and you can call it from any file to access the same object.

Example: Create two files in a folder. In the first file, we will do this:

• Define a value.
• Set a timeout to change the value after some time
• Export the value itself
• Export a function that returns the value

values.js

let x = 0 ; // set initial value
setTimeout(() => { x = 5; }, 2000); // sometime later, value will change

const getValueOfX = () => { return x; }; 

module.exports = {
    x: x,
    getValueOfX: getValueOfX
}; 

Now in the other file, we just import the two exports from the previous file (we put them both in an object for easy exporting). We can then log them out, wait for some time to pass, and log them out again.

index.js

let values = require('./values');

console.log(`Single value test. x = ${values.x}`);
console.log(`Function return value test. x = ${values.getValueOfX()}`);
setTimeout(() => { console.log(`Single value test. x = ${values.x}`); }, 4000);
setTimeout(() => { console.log(`Function return value test. x = ${values.getValueOfX()}`); }, 4000);

To run the code, just open your Terminal or Command Prompt and, from the same directory as these two files, run node index.js

You'll see that when just the value (object, array, w/e) is exported, it is exported as-is when the export runs - almost always before the API call is finished.

BUT - If you export a function that returns the value (object, array, w/e), then that function will retrieve the up-to-date version of the value at the time it is called! Great for API calls!

so your code might look like this:

let secrets = { jwtHash: 10 };
const client = new AWS.SecretsManager({
    region: region
});

let pool = null; 

client.getSecretValue({ SecretId: secretName }, async (err, data) => {
    if (err) {
        reject(err);
    } else {
        const res = await JSON.parse(data.SecretString);
        pool = new Pool({
            user: res.username,
            host: res.host
            database: res.dbname
            password: res.password
            port: res.port
        }); 
        pool.on('error', err=> {
            console.error('Unexpected error on idle client', err);
            process.exit(-1);
        }); 
    }
});

module.exports = function(){ return pool; };