Common memory leak patterns in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a timer that repeats every second.

Node.js

setInterval(() => { console.log('Tick'); }, [1]);

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

A10

B100

C1000

D5000

Attempts:

3 left

💡 Hint

Common Mistakes

Using 100 instead of 1000 causes the timer to tick too fast.

Using 5000 makes the timer tick every 5 seconds, not 1.

The setInterval function takes the delay in milliseconds. 1000 ms means 1 second.

2fill in blank

medium

Complete the code to remove the event listener properly.

Node.js

emitter.on('data', handler);
// Later remove listener
emitter.[1]('data', handler);

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

AremoveListener

BaddListener

Cemit

Donce

Attempts:

3 left

💡 Hint

Common Mistakes

Using addListener again adds more listeners, causing leaks.

Using emit triggers events but does not remove listeners.

To avoid memory leaks, remove event listeners with removeListener when no longer needed.

3fill in blank

hard

Fix the error in the code to avoid a memory leak caused by global variables.

Node.js

global.cache = {};
function addToCache(key, value) {
  [1].cache[key] = value;
}

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

Awindow

Bcache

Cthis

Dglobal

Attempts:

3 left

💡 Hint

Common Mistakes

Using window causes errors because it is a browser object.

Using this may not refer to the global object here.

In Node.js, global is the global object. Using it explicitly avoids confusion and leaks.

4fill in blank

hard

Fill both blanks to create a WeakMap and store an object without preventing garbage collection.

Node.js

const cache = new [1]();
const obj = {};
cache.[2](obj, 'data');

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

AWeakMap

BMap

Cset

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using Map keeps strong references, causing leaks.

Using add is not a method of Map or WeakMap.

A WeakMap allows objects to be garbage collected if no other references exist. Use set to add entries.

5fill in blank

hard

Fill all three blanks to create a closure that does not cause a memory leak by holding unnecessary references.

Node.js

function createCounter() {
  let count = 0;
  return function() {
    count [1] 1;
    return [2];
  };
}
const counter = createCounter();
counter(); // [3]

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

A+=

Bcount

C1

D++

Attempts:

3 left

💡 Hint

Common Mistakes

Using ++ alone without return causes confusion.

Returning 1 always does not reflect the count.

Use count += 1 to increment, return count, and calling counter() returns 1.