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Pascual Vila

Frontend Instructor // Code Syllabus

Common Pitfalls & Errors

The Error //

Generating a correlation ID but forgetting to forward it as a header on outbound calls to downstream services

// Wrong: the ID never leaves this service
await fetch(downstreamUrl); // no correlation header forwarded

// Correct
await fetch(downstreamUrl, { headers: { "x-request-id": req.id } });

The Solution //

A correlation ID that lives only in one service's own logs provides no value for tracing a request across a microservices architecture — the whole point is threading the same ID through every service the request touches. Explicitly include it as a header on every outbound HTTP call made while handling that request.

The Error //

Manually threading a request ID through every function parameter instead of using AsyncLocalStorage

// Tedious and error-prone: threading a parameter everywhere
function processOrder(order, requestId) { chargeCard(order, requestId); }

// Cleaner: AsyncLocalStorage makes it implicitly available
function processOrder(order) { chargeCard(order); } // requestId available via als.getStore()

The Solution //

Passing req.id as an extra parameter through every function in a call chain is tedious, easy to forget in a new function, and clutters function signatures with a cross-cutting concern unrelated to their actual purpose. AsyncLocalStorage maintains the context implicitly across async operations without explicit parameter threading.