setTimeout and clearTimeout in Node.js - Mini Project: Build & Apply

Using setTimeout and clearTimeout in Node.js

📖 Scenario: You are creating a simple Node.js script that waits a few seconds before showing a message. Sometimes, you want to stop the waiting if something changes.

🎯 Goal: Build a Node.js script that sets a timer to print a message after 3 seconds, but also allows canceling the timer before it runs.

📋 What You'll Learn

Create a timer using setTimeout that waits 3 seconds

Store the timer ID in a variable called timerId

Create a variable called cancelAfter set to 2000 (milliseconds)

Use setTimeout again to cancel the first timer after cancelAfter milliseconds using clearTimeout

Ensure the message only prints if the timer is not canceled

💡 Why This Matters

🌍 Real World

Timers are used in Node.js to delay actions, like waiting for a response or scheduling tasks.

💼 Career

Understanding timers and how to cancel them is important for writing efficient asynchronous code in Node.js applications.

1

Create a timer with setTimeout

Create a variable called timerId and assign it the result of setTimeout that waits 3000 milliseconds and then runs a function that logs the string 'Timer done!'.

Node.js

// Your code here

Need a hint?

Use setTimeout with a function and 3000 milliseconds. Save the returned ID in timerId.

2

Add a cancelAfter variable

Add a variable called cancelAfter and set it to 2000 (milliseconds).

Node.js

const timerId = setTimeout(() => {
  console.log('Timer done!');
}, 3000);

// Your code here

Need a hint?

Just create a variable cancelAfter and assign it the number 2000.

3

Use setTimeout to cancel the first timer

Use setTimeout with a function that calls clearTimeout(timerId) after cancelAfter milliseconds.

Node.js

const timerId = setTimeout(() => {
  console.log('Timer done!');
}, 3000);

const cancelAfter = 2000;

// Your code here

Need a hint?

Use setTimeout with a function that calls clearTimeout(timerId) after cancelAfter milliseconds.

4

Complete the script to show timer cancellation

Add a console.log statement before the cancel timeout that logs the string 'Timer will be canceled after 2000ms'.

Node.js

const timerId = setTimeout(() => {
  console.log('Timer done!');
}, 3000);

const cancelAfter = 2000;

// Your code here

setTimeout(() => {
  clearTimeout(timerId);
}, cancelAfter);

Need a hint?

Use console.log to show a message before the cancel timeout runs.