Serving a GET request with nested callbacks - node.js

Question

I have a generic Node+Express server where I serve GET requests. Some of these GET requests need multiple DB queries which are callbacks.
Here is an example of my code:
GET router:
router.get('/getbalance', function(req, res, next) {
wallet.createNewAddress()
.then(result => {
res.send(result);
})
.catch(err => {
console.log(err);
});
This is the function with callbacks:
async createNewAddress()
{
pool.query(`SELECT ...`)
.then (dbres1 => {
pool.query(`SELECT ...`)
.then(dbres2 => {
(async() => {
var pubkeys = await this.getPublicKeysFromIndexes(wallet.id, index_wallet_1, index_wallet_2, index_wallet_3);
var script = this.generateScript(pubkey1, pubkey2, pubkey3);
})();
})
.catch(e => {
console.log(e.stack);
})
}
})
.catch(e => {
console.log(e.stack);
});
}
I have removed long statements for brevity.
As you can see, I have multiple levels of nested promises.
What is the proper way to handle a request like this? Should I return each promise or should I run everything synchronously using async()?
What I need to do is to return the script at the very middle of the statements. This last call that returns the script is a normal synchronous function.
Appreciate any advice.
Thank you.

Answer 1

I believe using async/await will give you much more readable code, while essentially following the same logic. Of course you will have to be aware that you'll need to add try/catch handler(s) to the code.
If you use async/await you'll end up with something like this:
async function createNewAddress()
{
try {
let dbres1 = await pool.query(`SELECT ...`);
let dbres2 = await pool.query(`SELECT ...`);
var pubkeys = await this.getPublicKeysFromIndexes(wallet.id, index_wallet_1, index_wallet_2, index_wallet_3);
return this.generateScript(pubkey1, pubkey2, pubkey3);;
} catch (err) {
// ok something bad happened.. we could skip this handler and let the error bubble up to the top level handler if we're happy with that approach.
console.error(err);
// Rethrow or create new error here.. we don't want to swallow this.
throw err;
}
}
You can then call as before:
router.get('/getbalance', function(req, res, next) {
wallet.createNewAddress()
.then(result => {
res.send(result);
})
.catch(err => {
console.log(err);
});
Or use an async handler:
router.get('/getbalance', async function(req, res, next) {
try {
let result = await wallet.createNewAddress();
res.send(result);
} catch (err) {
// Also consider sending something back to the client, e.g. 500 error
console.log(err);
};
})