JavaScript asynchronous flow control is the core mechanism for handling non-blocking operations in a single-threaded language. Early implementations used callback functions but often led to callback hell, making code difficult to maintain. Promises provided a more elegant chaining solution. The ES2017 introduction of async/await syntax allowed asynchronous code to be written with synchronous-like readability. Parallel control can be achieved using Promise.all to execute multiple asynchronous operations simultaneously. Advanced scenarios requiring strategies like throttling or retries can leverage libraries like async.js or custom implementations. The event-driven pattern is suitable for handling multiple asynchronous events. Generator functions combined with Promises can achieve coroutine-like effects. Error handling requires global catching and middleware interception. Performance optimization must consider concurrency control and batch processing. These techniques are widely used in web development, including API calls, database operations, and file processing scenarios.
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JavaScript asynchronous error handling faces numerous challenges, including the distinct mechanisms of callbacks, Promises, and async/await. Uncaught errors may lead to silent failures. Callbacks use the error-first pattern, with common issues such as forgetting to check error parameters and callback hell. Promises capture errors via the `catch` method, and unhandled rejections generate warnings. Async/await requires `try-catch` for error handling, while global error handlers can catch uncaught exceptions. Custom error types enable precise handling. In production, errors should be logged to monitoring systems. Testing asynchronous errors requires validating throws and handling. Performance considerations call for optimizing hot-path error handling. Differences exist between browser and Node.js environments, and third-party libraries follow their own conventions. Error recovery strategies, such as retry mechanisms, can be employed. Large-scale applications may design a centralized error-handling architecture.
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