Express: send response after getting another response via an api call - node.js

Question

I want my website to respond after a successful api call, which is initiated via a post request and also changes some database values.
If there was NO post request the site should also load as usual.
If I do something like this, then the site is getting loaded as usual and then I get an error because of the second rendering attempt.
I guess because node does wait for the receipt, but in parallel does already execute the loadNewSite() function:
app.all('/customer', function(req, res) {
if (Object.keys(req.body).length != 0) {
apiCall(someParameter)
.on('error', error => {console.log(error);} )
.on('receipt', function() {loadNewSite();} );
}
function loadNewSite() {
return res.render('site.html');
}
loadNewSite()
})

Answer 1

try removing the last loadNewSite() as one is already called when you on reciept
check with req.method whether it's a POST request or not.
app.all('/customer', function(req, res) {
// if method is not post handle seperately
if(req.method != 'POST'){
return loadNewSite('site.html');
}
if (Object.keys(req.body).length != 0) {
apiCall(someParameter)
.on('error', error => {console.log(error);} )
.on('receipt', function() {loadNewSite();} );
}
function loadNewSite() {
return res.render('site.html');
}
})

Answer 2

I would create a promise to execute the Api call and resolve it on receipt or reject it on error. Then make the callback async and await for the api call promise.
I left the final call to loadNewSite in case of error, obviously you can modify it and make a function that maybe returns something different in error case.
const execApiCall = (params) => {
return new Promise((resolve, reject) => {
apiCall(params)
.on('error', error => {reject(error);} )
.on('receipt', function() {resolve();} );
})
};
app.all('/customer', async function(req, res) {
function loadNewSite() {
return res.render('site.html');
}
if (Object.keys(req.body).length != 0) {
try {
await execApiCall(params);
return loadNewSite();
} catch (e) { //handle errors }
}
loadNewSite()
})