JavaScript setTimeout() Timer

setTimeout() schedules a function to run once after at least the specified delay. It is useful for reminders, delayed UI actions, debouncing, and scheduling the next step of recurring work.

setTimeout(() => {
  console.log("Runs once after about 2 seconds");
}, 2000);

setTimeout() Syntax and Return Value Top ↑

const timeoutId = setTimeout(callback, delay);

The delay is in milliseconds and the return value is a timeout ID that can be passed to clearTimeout().

Pass a Function Instead of a String Top ↑

function showReminder() {
  console.log("Take a break");
}
setTimeout(showReminder, 5000);

Avoid older string forms such as setTimeout('showReminder()', 5000).

Cancel a Pending Timeout Top ↑

const id = setTimeout(showReminder, 5000);
clearTimeout(id);

Pass Arguments to the Callback Top ↑

function notify(message) {
  console.log(message);
}
setTimeout(notify, 1000, "Done");

The Delay Is a Minimum, Not an Exact Appointment Top ↑

The callback becomes eligible to run after the delay. A busy main thread, browser scheduling, or background-tab throttling can make it run later. For a deadline, compare the current time with the target time instead of counting timeout calls.

What Does setTimeout(..., 0) Mean? Top ↑

A zero delay does not run the callback immediately or before the current JavaScript finishes. It schedules the callback for a later task when the event loop is able to run it.

console.log("A");
setTimeout(() => console.log("C"), 0);
console.log("B");
// A, B, then C

Use setTimeout() Recursively for Controlled Repetition Top ↑

function repeat() {
  doWork();
  setTimeout(repeat, 1000);
}

See recursive setTimeout(). For fixed repeating callbacks, see setInterval().

Simple Reminder with User-Selected Delay Top ↑

const seconds = Number(delayInput.value);
if (Number.isFinite(seconds) && seconds >= 0) {
  setTimeout(() => alert("Reminder"), seconds * 1000);
}

If the reminder must survive a reload or browser restart, save an absolute target timestamp and recompute the remaining time after loading; a plain in-memory timeout is not persistent.

Common setTimeout() Mistakes Top ↑

• Passing the result of a function call instead of the function itself.
• Using strings as code.
• Assuming millisecond-perfect execution.
• Forgetting to cancel timers when a UI action is abandoned.
• Using a timeout as durable scheduling for tasks that must survive navigation or shutdown.

Related: periodic click example, window alert, stopwatch.

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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