The event loop is actually composed of one or more event queues. In each queue, events are handled in a FIFO order. It's up to the browser to decide how many queues to have and what form of prioritisation to give them.

Dec 5, 2018 · Task queues are used by user agents to coalesce task sources within a given event loop. Example. For example, a user agent could have one task queue for mouse and key events (to which the user interaction task source is associated), and another to which all other task sources are associated.

Jul 12, 2023 · What is the exact priority of callback functions triggered using addEventListener compared to microtask and macrotask queue callbacks in the Event Loop? In other words, during which exact phase of the Event Loop are they dequeued from their respective queues?

Dec 20, 2023 · Priority Queue is an extension of Queue having some properties as follows: Each element of the priority queue has a priority associated with it. Elements are added to the queue as per priority. Lowest priority elements are removed first.

Mar 31, 2024 · It turns out there are different priorities for different tasks in the task queue. Have you ever thought in which priority they are being executed? Does the browser use the same priority for...

Aug 28, 2023 · When a promise settles, its .then() or .catch() handlers are added to the microtask queue, which, as mentioned earlier, has a priority over the regular task queue. .then(val => { }) .then(val =>...

Dec 16, 2024 · Microtask Queue: A higher-priority queue for promises and MutationObserver callbacks. Microtasks are executed before tasks in the task queue. Event Loop: Continuously checks if the call stack...

Mar 13, 2025 · By mastering the Call Stack, Web APIs, Callback Queue, and Priority Queue, you can write more efficient, non-blocking JavaScript applications. Keep experimenting with different scenarios, optimize your event handling strategies, and apply best practices to …

Sep 19, 2012 · If an event fires (or a callback's timeout period times out), its handler will be executed if nothing is going on, i.e. if the event loop is idle. However, if the timeout fires, and the javascript event loop is busy, the callback (and any subsequent events ready to be handled etc) will be put on a queue till the event loop is free to execute them.

Mar 23, 2024 · The event loop is the heart of JavaScript’s concurrency model. It continuously checks the call stack and task queues, ensuring that the execution of code remains non-blocking. It follows...