setTimeout

setTimeout is a timer function available in web browsers and Node.js that schedules the execution of a function after a specified delay. When invoked, it places the callback into the event loop's task queue to be run once the delay elapses. The call is asynchronous relative to the code that set it, allowing the rest of the program to continue executing.

Syntax: setTimeout(callback, delay, [arg1, arg2, ...]). Callback is invoked after delay milliseconds, optionally with the provided arguments. The function returns a timer identifier, which can be used with clearTimeout to cancel the scheduled callback before it fires. Delay is measured in milliseconds; a delay of 0 yields execution as soon as the current call stack is cleared in most environments.

In browsers, timer precision is not guaranteed. Timers may be clamped or throttled in inactive tabs or complex environments, causing delays longer than requested. For 0 or small delays, the timer may still be deferred to the next event loop cycle. setTimeout is single-shot; to execute repeatedly at a fixed rate, use setInterval or recursively schedule subsequent timeouts.

Usage includes delaying actions, debouncing user input, and scheduling work to occur later in the event loop. It is distinct from setInterval, which repeats until cleared. ClearTimeout cancels a pending timeout. In Node.js, setTimeout is part of the timers API and behaves similarly to its browser counterpart for scheduling a callback.