event loop
compound.compound. a system in a computer program that waits for things to happen, like a mouse click, and then runs the right code to handle them. It keeps the program running and responsive by checking for new tasks in a continuous circle.
compound. a programming construct that waits for and dispatches events or messages in a program. It functions by making a request to some internal or external event provider, which generally blocks until an event has arrived, and then calls the relevant event handler.
The event loop handles user clicks while the page loads.
Because JavaScript runs on a single thread, the event loop is responsible for executing code, collecting events, and executing queued sub-tasks.
Efficiently managing the event loop is critical in asynchronous programming to ensure that long-running operations do not block the main execution thread and degrade the user experience.
A compositional term formed from the noun event, denoting a discrete occurrence or signal, and the noun loop, referring to a sequence of instructions that repeats until a condition is met.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.
Commonly used in the context of web development, specifically regarding the JavaScript execution model.
Last updated July 22, 2026