setInterval and clearInterval in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to run a function every 2 seconds using setInterval.

Node.js

const intervalId = setInterval([1], 2000);

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

A() => console.log('Hello')

Bconsole.log('Hello')

Cconsole.log

DsetTimeout

Attempts:

3 left

💡 Hint

Common Mistakes

Passing console.log('Hello') directly runs it once instead of repeatedly.

Passing setTimeout instead of setInterval.

The setInterval function expects a function as its first argument. Using an arrow function () => console.log('Hello') correctly passes a function to run every 2 seconds.

2fill in blank

medium

Complete the code to stop the interval after 5 seconds using clearInterval.

Node.js

const intervalId = setInterval(() => console.log('Tick'), 1000);
setTimeout(() => [1](intervalId), 5000);

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

AstopInterval

BsetInterval

CclearTimeout

DclearInterval

Attempts:

3 left

💡 Hint

Common Mistakes

Using clearTimeout instead of clearInterval.

Trying to call setInterval again to stop it.

To stop a repeating interval, use clearInterval with the interval ID.

3fill in blank

hard

Fix the error in the code to correctly stop the interval after 3 seconds.

Node.js

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

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

AintervalId

Bid

CsetInterval

DclearInterval

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a wrong variable name.

Using clearTimeout instead of clearInterval.

The variable id holds the interval ID. Pass it to clearInterval to correctly stop the interval after 3 seconds.

4fill in blank

hard

Fill both blanks to create an interval that logs 'Hi' every second and stops after 4 seconds.

Node.js

const [1] = setInterval(() => console.log('Hi'), 1000);
setTimeout(() => [2]([1]), 4000);

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

AintervalId

BclearInterval

CsetInterval

DtimeoutId

Attempts:

3 left

💡 Hint

Common Mistakes

Using setInterval instead of clearInterval to stop.

Using a variable name that doesn't match.

We store the interval ID in intervalId. To stop it, we call clearInterval(intervalId).

5fill in blank

hard

Fill all three blanks to create an interval that counts seconds and stops after 3 counts.

Node.js

let count = 0;
const [1] = setInterval(() => {
  [2];
  console.log(count);
  if (count === 3) {
    [3]([1]);
  }
}, 1000);

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

AintervalId

B++count

CclearInterval

Dcount++

Attempts:

3 left

💡 Hint

Common Mistakes

Using pre-increment (++count) instead of post-increment (count++).

Using clearTimeout instead of clearInterval.

We store the interval ID in intervalId. We increment count with count++. When count reaches 3, we stop the interval with clearInterval(intervalId).

Practice

1. What does the setInterval function do in Node.js?

easy

A. Runs a function only once after a delay

B. Stops a running timer

C. Runs a function repeatedly at specified time intervals

D. Schedules a function to run immediately

Solution

1. Step 1: Understand setInterval purpose

   setInterval schedules a function to run repeatedly every specified milliseconds.

2. Step 2: Compare with other timer functions

   setTimeout runs once after delay, clearInterval stops intervals.

3. Final Answer:

   Runs a function repeatedly at specified time intervals -> Option C

4. Quick Check:

   setInterval = repeated execution [OK]

Hint: setInterval repeats; setTimeout runs once [OK]

Common Mistakes:

• Confusing setInterval with setTimeout
• Thinking clearInterval starts timers
• Believing setInterval runs only once

2. Which of the following is the correct syntax to stop a repeating timer started with setInterval?

easy

A. clearInterval(timerId);

B. stopInterval(timerId);

C. clearTimeout(timerId);

D. cancelInterval(timerId);

Solution

1. Step 1: Identify the function to stop intervals

   clearInterval is the built-in function to stop intervals.

2. Step 2: Check other options

   clearTimeout stops timeouts, others are invalid functions.

3. Final Answer:

   clearInterval(timerId); -> Option A

4. Quick Check:

   clearInterval stops intervals [OK]

Hint: Use clearInterval with the interval ID [OK]

Common Mistakes:

• Using clearTimeout to stop intervals
• Using non-existent functions like stopInterval
• Not passing the timer ID to clearInterval

3. What will the following code output to the console?

let count = 0;
const id = setInterval(() => {
  count++;
  console.log(count);
  if (count === 3) clearInterval(id);
}, 1000);

medium

A. 1 2 3 (each number printed every second, then stops)

B. 1 2 3 4 5 (prints numbers every second indefinitely)

C. Only 3 printed once after 3 seconds

D. No output because clearInterval is called immediately

Solution

1. Step 1: Trace the interval execution

   Every 1000ms, count increases and prints. When count reaches 3, clearInterval stops it.

2. Step 2: Understand stopping condition

   After printing 3, the interval stops, so no further output.

3. Final Answer:

   1 2 3 (each number printed every second, then stops) -> Option A

4. Quick Check:

   Interval runs 3 times then stops [OK]

Hint: clearInterval inside callback stops after condition [OK]

Common Mistakes:

• Assuming it runs forever
• Thinking clearInterval stops immediately before first print
• Confusing setTimeout with setInterval

4. Identify the error in this code snippet:

const id = setInterval(() => {
  console.log('Hello');
});
clearInterval(id);

medium

A. No error, code works fine

B. clearInterval should be called inside the callback

C. setInterval cannot be assigned to a variable

D. Missing interval time argument in setInterval

Solution

1. Step 1: Check setInterval syntax

   setInterval requires two arguments: function and interval time in milliseconds.

2. Step 2: Analyze the code

   Here, the interval time is missing, causing a syntax error or unexpected behavior.

3. Final Answer:

   Missing interval time argument in setInterval -> Option D

4. Quick Check:

   setInterval needs delay argument [OK]

Hint: Always provide delay time in setInterval [OK]

Common Mistakes:

• Omitting the delay argument
• Calling clearInterval immediately without delay
• Thinking setInterval returns undefined

5. You want to print "Tick" every second but stop after 5 ticks. Which code correctly achieves this?

hard

A. setInterval(() => {
console.log('Tick');
clearInterval(timer);
}, 1000);

B. let ticks = 0;
const timer = setInterval(() => {
ticks++;
console.log('Tick');
if (ticks === 5) clearInterval(timer);
}, 1000);

C. let ticks = 0;
setTimeout(() => {
console.log('Tick');
if (ticks < 5) ticks++;
}, 1000);

D. const timer = setInterval(() => {
console.log('Tick');
if (ticks === 5) clearTimeout(timer);
}, 1000);

Solution

1. Step 1: Identify correct interval and stopping logic

   let ticks = 0; const timer = setInterval(() => { ticks++; console.log('Tick'); if (ticks === 5) clearInterval(timer); }, 1000); uses setInterval with a counter and calls clearInterval after 5 ticks.

2. Step 2: Check other options for errors

   setInterval(() => { console.log('Tick'); clearInterval(timer); }, 1000); clears immediately, let ticks = 0; setTimeout(() => { console.log('Tick'); if (ticks < 5) ticks++; }, 1000); uses setTimeout wrongly, const timer = setInterval(() => { console.log('Tick'); if (ticks === 5) clearTimeout(timer); }, 1000); uses clearTimeout instead of clearInterval.

3. Final Answer:

   let ticks = 0; const timer = setInterval(() => { ticks++; console.log('Tick'); if (ticks === 5) clearInterval(timer); }, 1000); -> Option B

4. Quick Check:

   Use counter and clearInterval after limit [OK]

Hint: Use a counter and clearInterval after limit [OK]

Common Mistakes:

• Calling clearInterval immediately
• Using clearTimeout to stop intervals
• Using setTimeout instead of setInterval for repeated tasks