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.
Recommended
All combinators
Pick
Simulated promises
Timeline (0–3s). Filled bar = settled. Hatched = rejected.
Combined promise
— at ms
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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