Sequential vs parallel execution in Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

Javascript

function first() {
  console.log('First');
}

function second() {
  console.log('Second');
}

first();
[1]();

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

Asecond

BsetTimeout

CPromise

Dasync

Attempts:

3 left

💡 Hint

Common Mistakes

Using setTimeout or Promise here causes asynchronous behavior, not sequential direct calls.

Forgetting to add parentheses to call the function.

Calling second() after first() runs the functions one after the other, which is sequential execution.

2fill in blank

medium

Complete the code to run two asynchronous functions in parallel using Promise.all.

Javascript

function task1() {
  return new Promise(resolve => setTimeout(() => resolve('Task 1 done'), 1000));
}

function task2() {
  return new Promise(resolve => setTimeout(() => resolve('Task 2 done'), 500));
}

Promise.[1]([task1(), task2()]).then(results => {
  console.log(results);
});

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

Arace

Bcatch

Cthen

Dall

Attempts:

3 left

💡 Hint

Common Mistakes

Using Promise.race runs only the first promise that finishes.

Using then or catch directly on Promise does not run multiple promises.

Promise.all runs multiple promises in parallel and waits for all to finish before continuing.

3fill in blank

hard

Fix the error in the async function to run tasks sequentially using await.

Javascript

async function runTasks() {
  const result1 = task1();
  const result2 = task2();
  console.log(await result1);
  console.log(await result2);
}

runTasks();

// Fix the line: const result1 = [1];

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

AsetTimeout(task1, 1000)

Bawait task1()

Ctask1()

DPromise.resolve(task1())

Attempts:

3 left

💡 Hint

Common Mistakes

Not using await causes the tasks to start but not wait for completion.

Using setTimeout does not return a promise and won't work with await.

Using await before task1() ensures the function waits for task1 to finish before continuing, enabling sequential execution.

4fill in blank

hard

Fill both blanks to create a function that runs two tasks in parallel and logs their results.

Javascript

async function runParallel() {
  const [result1, result2] = await Promise.[1]([task1(), task2()]);
  console.log(result1);
  console.log([2]);
}

runParallel();

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Aall

Bresult2

Crace

Dresult1

Attempts:

3 left

💡 Hint

Common Mistakes

Using Promise.race only waits for the first task to finish.

Logging result1 twice misses the second task's result.

Promise.all runs tasks in parallel. Logging result1 and result2 shows both results after completion.

5fill in blank

hard

Fill all three blanks to create a function that runs tasks sequentially using await and logs results.

Javascript

async function runSequential() {
  const result1 = await [1]();
  console.log(result1);
  const result2 = await [2]();
  console.log([3]);
}

runSequential();

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Atask1

Btask2

Cresult2

Dresult1

Attempts:

3 left

💡 Hint

Common Mistakes

Calling tasks without await runs them in parallel.

Logging the wrong result variable causes confusion.

Awaiting task1 and task2 runs them one after the other. Logging result1 and result2 shows their outputs in order.