Event loop phases and timer execution in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to schedule a function to run after 1000 milliseconds.

Node.js

setTimeout(() => { console.log('Hello after 1 second'); }, [1]);

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Anull

B10

C0

D1000

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or null will cause the callback to run immediately or not at all.

Confusing seconds with milliseconds.

The setTimeout function schedules the callback to run after the specified milliseconds. Here, 1000 means 1 second delay.

2fill in blank

medium

Complete the code to schedule a function to run repeatedly every 500 milliseconds.

Node.js

const intervalId = setInterval(() => { console.log('Repeating every 0.5 seconds'); }, [1]);

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A500

B1000

C50

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 will cause the callback to run as fast as possible, which is not intended.

Confusing interval time with timeout delay.

The setInterval function runs the callback repeatedly every given milliseconds. 500 means every half second.

3fill in blank

hard

Fix the error in the code to clear the interval after 3 seconds.

Node.js

const id = setInterval(() => { console.log('Tick'); }, 1000);
setTimeout(() => { clearInterval([1]); }, 3000);

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AtimerId

BintervalId

Cid

DtimeoutId

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name that was never declared.

Confusing interval ID with timeout ID.

The setInterval returns an ID which must be passed to clearInterval to stop it. Here, the ID is stored in id.

4fill in blank

hard

Fill both blanks to create a Promise that resolves after 2 seconds using setTimeout.

Node.js

const delay = ms => new Promise(resolve => {
  setTimeout(() => {
    [1]();
  }, [2]);
});

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Aresolve

Bms

Cconsole.log

DclearTimeout

Attempts:

3 left

💡 Hint

Common Mistakes

Calling reject instead of resolve.

Using console.log instead of resolve.

Passing wrong delay time.

Inside the Promise, resolve is called to mark it as done. The delay time is passed as milliseconds to setTimeout.

5fill in blank

hard

Fill all three blanks to create a map of words to their lengths, but only for words longer than 3 characters.

Node.js

const words = ['apple', 'bat', 'carrot', 'dog'];
const lengths = words.reduce((acc, [3]) => {
  if ([3].length > 3) {
    acc[[1]] = [2];
  }
  return acc;
}, {});

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Aword

Bword.length

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names.

Using length as key instead of word.

Not filtering words by length.

The reduce method creates an object that maps each word to its length word.length for words longer than 3 characters.