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Testing Async Code, Timers, and Errors thumbnail

Testing Async Code, Timers, and Errors

This is Part 5 of the “Frontend Testing, Done Right” series. Browse the full series · Glossary Real-world code waits. It waits for API responses; it waits for timers. That makes async testing the first wall most frontend developers hit — but the reason it feels hard boils down to a single question: “when do you verify?” Grade the answer sheet before the answer arrives, and you’re grading a blank page. This one article packs the complete toolkit for code that waits: Promise verification (resolves/rejects), fake timers, and the failure cases. ...

Published date: 2026-07-08 · Reading time: 9 min · Word count: 1745 words · Author: Isaac
Promise.all vs Promise.allSettled: The Difference That Matters thumbnail

Promise.all vs Promise.allSettled: The Difference That Matters

I built a dashboard. I was proud of it. Three lines of code using Promise.all to fetch three APIs at once — and the code review feedback was “clean.” Multiple tasks running concurrently - with Promise.all, one failure affects the whole thing Photo: Unsplash javascript Read line numbers: OFF Line-number reading help Reading line numbers aloud This button is for screen reader users. ...

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