Event loop mental model in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to schedule a function to run after the current event loop phase.

Node.js

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

Drag options to blanks, or click blank then click option'

A0

B1000

Cnull

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using negative or null values for delay causes errors or unexpected behavior.

Using 0 as the delay schedules the function to run after the current event loop phase.

2fill in blank

medium

Complete the code to add a callback to the next tick queue.

Node.js

process.[1](() => { console.log('Next tick'); });

Drag options to blanks, or click blank then click option'

AnextTick

BsetInterval

CsetTimeout

DsetImmediate

Attempts:

3 left

💡 Hint

Common Mistakes

Using setImmediate or setTimeout delays the callback to later phases.

process.nextTick schedules a callback to run immediately after the current operation, before other event loop phases.

3fill in blank

hard

Fix the error in the code to correctly schedule a callback after the current timers phase.

Node.js

setImmediate(() => { console.log('Immediate'); });
setTimeout(() => { console.log('Timeout'); }, [1]);

Drag options to blanks, or click blank then click option'

A-1

B0

Cundefined

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using null or negative values for timeout delay.

Using 0 as the delay in setTimeout schedules the callback after the current timers phase, matching expected behavior.

4fill in blank

hard

Fill both blanks to create a map of timers with delays and their callback names.

Node.js

const timers = { [1]: 'first', [2]: 'second' };

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A100

BsetTimeout

C200

DsetImmediate

Attempts:

3 left

💡 Hint

Common Mistakes

Using function names as keys instead of numbers.

The keys are timer delays in milliseconds, so 100 and 200 are correct.

5fill in blank

hard

Fill all three blanks to create a filtered object of callbacks with delays greater than 100.

Node.js

const filtered = Object.entries(timers).reduce((acc, [[1], [2]]) => {
  if ([1] [3] 100) {
    acc[[1]] = [2];
  }
  return acc;
}, {});

Drag options to blanks, or click blank then click option'

Adelay

Bcb

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names or wrong comparison operators.

The reduce uses delay as key, cb as value, and filters delays greater than 100.