How do you limit concurrency in Node.js?
Process items in batches: slice the array into chunks of N, use Promise.all for each batch, and await each batch before processing the next. Or use a library like p-limit or Bluebird's Promise.map with concurrency option.
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More FAQs in Node.js Async Programming Interview Questions Promises, Async/Await, and Callbacks
Callback hell is deeply nested callbacks (pyramid of doom) when multiple async operations depend on each other. Fix it by using Promises (.then chains) or async/await (makes async code look synchronous with try-catch). Extract logic into named functions for readability.
Promise.all: all must succeed, or all fail (fast fail). allSettled: all complete regardless of success/failure (returns status and value/reason for each). race: first to complete wins (success or failure). Use all for parallel independent operations, allSettled when you want all results, race for timeouts.
Use try-catch blocks around await calls. Catch the error, log it, and either re-throw it (for the caller to handle) or return a default value. For unhandled rejections, add process.on('unhandledRejection', handler) as a safety net.
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