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You reach for `Promise.all` for every concurrent request. Here's when to use the other three.

Parsa Jiravand 2026年07月13日 17:36 4 次阅读 来源:Dev.to

Imagine you're loading a dashboard. Four widgets, four APIs, fire them all at once: const [ users , revenue , alerts , activity ] = await Promise . all ([ fetchUsers (), fetchRevenue (), fetchAlerts (), fetchActivity (), ]); The alerts API is occasionally slow and sometimes returns a 500. When it does, your entire dashboard fails. Not one broken widget — four broken widgets. Promise.all rejects on the first failure and takes the other three successful results with it into the void. You reached for the right primitive for concurrency, but the wrong one for this use case. The four methods and what they actually do JavaScript gives you four ways to run promises concurrently. They differ in one thing: what happens when a promise fails or resolves first. Method Resolves when Rejects when Promise.all All succeed Any one fails Promise.allSettled All finish (success or failure) Never Promise.any Any one succeeds All fail Promise.race Any one finishes Any one fails first The instinct to reach for Promise.all is understandable — it returns all the values in a single array and feels like the obvious way to "do these things at the same time." But concurrency and failure handling are two separate questions. Promise.all answers both at once, and the answer to the second one is often wrong for the situation you're in. 🎮 Try it yourself ▶️ Open the interactive playground → Runs right in your browser — poke at it and watch the concept react live. Promise.allSettled — partial success Promise.allSettled waits for every promise to settle — resolve or reject — and returns a result array describing what happened to each one: const results = await Promise . allSettled ([ fetchUsers (), fetchRevenue (), fetchAlerts (), fetchActivity (), ]); for ( const result of results ) { if ( result . status === ' fulfilled ' ) { console . log ( ' got data: ' , result . value ); } else { console . error ( ' failed: ' , result . reason ); } } Each element has a status of 'fulfilled' (with a value ) or 'r

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