Structured Concurrency in JavaScript: Beyond Promise.all

The Problem with Unstructured Async Code JavaScript async code has a scope problem. You fire off promises and hope they complete—or fail—cleanly. When something goes wrong mid-flight, cleanup is your responsibility. // Classic problem: partial failure async function loadDashboard(userId: string) { const [user, orders, analytics] = await Promise.all([ getUser(userId), getOrders(userId), // This throws after 2 seconds getAnalytics(userId), // This is still running! ]); // getAnalytics never gets cancelled } When getOrders rejects, Promise.all rejects—but getAnalytics keeps running in the background, consuming resources, potentially writing stale data. Promise.allSettled: Handle All Results async function loadDashboard(userId: string) { const results = await Promise.allSettled([ getUser(userId), getOrders(userId), getAnalytics(userId), ]); const [userResult, ordersResult, analyticsResult] = results; // Handle each independently const user = userResult.status === 'fulfilled' ? userResult.v