How to build a transaction system into a .then() chain? - node.js

Question

I have multiple chained, synchronous requests in my code. I am using the NodeJS package request-promise.
Here is some pseudocode to show how it is formatted:
initRequest.then(function(response){
return request2;
}).then(function(response2){
return request3;
}).then(function(response3){
return requestN;
}).catch(function(err){
log(error)
});
If, for example, request3 fails, what happens? Does the chain continue, or does it break out of the loop completely?
And if request2 was a POST, and request3 failed, is there a way to systematically roll back the data that request2 changed?
Thanks.

Answer 1

Does the chain continue, or does it break out of the loop completely?
It breaks and proceeds to catch or finally proposal, which is available in recent Node.js versions and polyfillable in older versions - similarly to how try..catch..finally works for synchronous code (this is how plain promises are translated to async functions as well).
And if request2 was a POST, and request3 failed, is there a way to systematically roll back the data that request2 changed?
This should be secured by a developer. If there's a possibility that data should be rolled back, necessary information (data entry ids) should be saved to variables and rolled back in catch.

Answer 2

if request3 fails, it will stop executing the rest of your request chains.
and there is no way to systematically rollback what request2 changed you would have to implement it your custom way.
to handle when request3 fails, catch request3 it self.
here is a simple/mini way to handle when request3 fails
initRequest.then(function(response){
return request2;
}).then(function(response2){
return request3.catch(function(err2){
//if something goes wrong do rollback
request2Rollback.then(rollbackRes => {
throw new Error("request3 failed! roll backed request 2!");
}).catch(function(err){
// the rollback itself has failed so do something serious here
throw err;
})
});;
}).then(function(response3){
return requestN;
}).catch(function(err){
log(error)
});