Promise Combinator Chooser & Visualizer
Pick the right combinator for your async pattern, then simulate 2–5 promises and watch when each settles and when the combined promise settles.
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Recommended
All combinators
Pick
Simulated promises
Timeline (0–3s). Filled bar = settled. Hatched = rejected.
Combined promise
— at ms
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About this tool
Promise.all, allSettled, race, and any look similar but behave differently on rejection and timing. The chooser maps your answers to a recommendation; the visualizer runs a deterministic simulation so you can see fail-fast vs first-success patterns.
Runs entirely in your browser. Config syncs to the URL.
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