setInterval and clearInterval in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does setInterval do in Node.js?

setInterval runs a function repeatedly at a fixed time interval until stopped.

beginner

How do you stop a repeating action started by setInterval?

You use clearInterval with the interval ID returned by setInterval.

beginner

What type of value does setInterval return?

It returns an interval ID (a number or object) that identifies the timer.

intermediate

Why should you always clear intervals when they are no longer needed?

To avoid memory leaks and unnecessary CPU usage by stopping the repeated function calls.

beginner

Write a simple example of setInterval and clearInterval usage.

<pre>const id = setInterval(() =&gt; {
  console.log('Hello every second');
}, 1000);

setTimeout(() =&gt; {
  clearInterval(id);
  console.log('Stopped interval');
}, 5000);</pre>

What does setInterval return when called?

A An ID to clear the interval later

B The result of the function called

C A promise that resolves after the interval

D Nothing (undefined)

setInterval returns an ID that you use with clearInterval to stop the repeated calls.

How do you stop a function from running repeatedly after using setInterval?

A Call <code>clearTimeout</code> with the interval ID

B Call <code>clearInterval</code> with the interval ID

C Call <code>stopInterval</code> with the function name

D Set the interval time to zero

clearInterval stops the repeated execution started by setInterval.

What happens if you never call clearInterval on a running interval?

A The interval automatically stops after 10 calls

B The function runs once and stops

C Node.js throws an error

D The function keeps running forever

The function will keep running repeatedly until you clear the interval or the program ends.

Which of these is a correct way to use setInterval?

A setInterval(() =&gt; console.log('Hi'), 1000);

B setInterval(console.log('Hi'), 1000);

C setInterval(console.log, 1000, 'Hi');

D setInterval('console.log("Hi")', 1000);

Passing a function reference or arrow function is correct. Option B calls the function immediately, not repeatedly.

What unit is the delay time in setInterval?

A Microseconds

B Seconds

C Milliseconds

D Minutes

The delay time is always in milliseconds (thousandths of a second).

Explain how setInterval and clearInterval work together in Node.js.

Think about starting and stopping a repeating alarm.

Describe why it is important to clear intervals when they are no longer needed.

Imagine leaving a timer running that you don’t need anymore.