JavaScript can run code later or repeatedly:
setTimeout(fn, ms): run once after a delay.setInterval(fn, ms): run repeatedly every ms milliseconds.clearTimeout(id)/clearInterval(id): cancel them.
1000 milliseconds = 1 second.
JavaScript Timing
setTimeout and setInterval.
✍️ 3 exercises + code challenge in this lessonKey Takeaways: JavaScript Timing
Mastering JavaScript Timing helps you write clean and reliable JavaScript code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.
JavaScript Timing Code Example
JavaScript<h1 id="clock">--:--:--</h1>
<p id="note"></p>
<button onclick="stop()">Stop clock</button>
<script>
const timer = setInterval(() => {
document.getElementById("clock").textContent = new Date().toLocaleTimeString();
}, 1000);
setTimeout(() => {
document.getElementById("note").textContent = "This message appeared after 2 seconds.";
}, 2000);
function stop() { clearInterval(timer); }
</script>
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JavaScript Timing Practice Exercises
Check what you learned in “JavaScript Timing”.
/ 3 solved
Fill in the blank
Run a function once after 2 seconds.
(showMessage, 2000);
✓ Correct!
Not quite. Try again.
Multiple choice
How do you stop a setInterval timer?
✓ Correct!
Not quite. Try again.
Code challenge
Use setTimeout to log "Done" after 300 milliseconds.
Write the code in the live editor. Your answer is checked automatically.
✓ Solved
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