Sequential vs parallel async execution in Node.js - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to run two async functions one after another (sequentially).

Node.js

async function runSequential() {
  await fetchData1();
  await [1]();
}

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

AfetchData2

BfetchData3

CfetchData1

DfetchData4

Attempts:

3 left

💡 Hint

Common Mistakes

Calling both functions without await causes parallel execution.

Forgetting to await the second function.

To run async functions sequentially, you await each one in order. Here, after fetchData1(), you await fetchData2().

2fill in blank

medium

Complete the code to run two async functions in parallel and wait for both to finish.

Node.js

async function runParallel() {
  await Promise.[1]([fetchData1(), fetchData2()]);
}

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

Aany

BallSettled

Crace

Dall

Attempts:

3 left

💡 Hint

Common Mistakes

Using Promise.race waits only for the first promise to settle.

Using Promise.any waits for the first fulfilled promise, not all.

Promise.all runs multiple promises in parallel and waits for all to resolve.

3fill in blank

hard

Fix the error in the code to correctly run async functions sequentially.

Node.js

async function run() {
  await fetchData1();
  [1] fetchData2();
}

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

Athen

Basync

Cawait

Dreturn

Attempts:

3 left

💡 Hint

Common Mistakes

Calling async functions without await runs them in parallel.

Using async keyword incorrectly inside the function body.

To run async functions sequentially, you must await each call to pause until it finishes.

4fill in blank

hard

Fill both blanks to create a parallel async execution that handles errors gracefully.

Node.js

async function runSafeParallel() {
  const results = await Promise.[1]([
    fetchData1(),
    fetchData2()
  ]);
  results.forEach(result => {
    if (result.status === '[2]') {
      console.log('Success:', result.value);
    } else {
      console.error('Error:', result.reason);
    }
  });
}

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

AallSettled

Bfulfilled

Crejected

Dresolved

Attempts:

3 left

💡 Hint

Common Mistakes

Using Promise.all rejects immediately on any error.

Checking for status 'resolved' instead of 'fulfilled'.

Promise.allSettled waits for all promises and returns their status. Checking for fulfilled lets you handle successes and errors separately.

5fill in blank

hard

Fill all three blanks to create a dictionary of results from parallel async calls filtering only successful ones.

Node.js

async function getResults() {
  const results = await Promise.[1]([
    fetchData1(),
    fetchData2(),
    fetchData3()
  ]);
  return results.reduce((acc, [2], index) => {
    if ([3].status === 'fulfilled') {
      acc[`data${index + 1}`] = [2].value;
    }
    return acc;
  }, {});
}

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

AallSettled

Bresult

Cresults

Dres

Attempts:

3 left

💡 Hint

Common Mistakes

Using Promise.all which rejects on first error.

Using wrong variable names causing runtime errors.

Promise.allSettled returns an array of result objects. Using result as the variable name for each item, you check if result.status is 'fulfilled' to include only successful results.