JavaScript Event Loop Explained: Microtasks, Macrotasks and Execution Order

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A detailed technical guide published on DEV Community breaks down how JavaScript's event loop manages code execution in single-threaded environments. The article explains that when the call stack empties, the loop follows a strict priority: synchronous code runs first, followed by all microtasks, a potential render phase, and then one macrotask at a time. Microtasks — sourced from Promises, queueMicrotask, and MutationObserver — always execute before macrotasks like setTimeout or DOM events. The guide uses step-by-step output prediction examples to illustrate how developers can mentally trace execution order in any JavaScript snippet. It also covers advanced topics including async/await behavior, Node.js event loop phases, Web Workers, and techniques for avoiding main-thread blocking.

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ProgrammingDEV Community ·

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