Loading... Login Loading... Register

JavaScript Event Loop and Asynchronous Programming Quiz

Want to learn more than this quiz offers you? Have a look at my Frontend web development courses.

Create an account and save your quiz results

Login and save your results

First Name *

Last Name *

Email *

Password *

Confirm Password *

I agree to the Terms of Service & Privacy Policy.

Add me to your newsletter.

Question 1/10

Which of the following statements about `setImmediate` in Node.js is true?

Select your answer

`setImmediate` schedules a function to be executed with zero delay

`setImmediate` runs before promise handlers in the microtask queue

`setImmediate` is an alias for `setTimeout(function, 0)`

`setImmediate` executes code in the next iteration of the event loop

Question 2/10

What is the primary role of the JavaScript event loop in the browser?

Select your answer

Managing synchronous code execution

Compiling JavaScript code into machine code

Handling asynchronous operations and executing callback functions

Managing static variable declarations

Question 3/10

What will the following code output to the console? Assume a Node.js environment.

console.log('First');

setTimeout(() => {
    console.log('Timeout');
}, 0);

setImmediate(() => {
    console.log('Immediate');
});

process.nextTick(() => {
    console.log('Next Tick');
});

console.log('Last');

Select your answer

First, Last, Next Tick, Immediate, Timeout

First, Last, Immediate, Next Tick, Timeout

First, Next Tick, Last, Immediate, Timeout

First, Last, Timeout, Immediate, Next Tick

Question 4/10

How does JavaScript handle I/O operations like reading files with respect to the event loop?

Select your answer

Using asynchronous callbacks that the event loop will execute when operations complete

Automatically converting them to synchronous operations

Queueing I/O operations in the microtask queue

By blocking the call stack until the operation completes

Question 5/10

Which of the following best describes event delegation in JavaScript?

Select your answer

Directly binding events to each individual element

Attaching an event listener to a common ancestor to handle events via propagation

Capturing all event listeners in a single callback and dispatching manually

Using `setTimeout` to handle asynchronous events

Question 6/10

In the JavaScript event loop model, what is the main purpose of the microtask queue?

Select your answer

To manage long-running tasks

To execute tasks immediately after the current operation completes, but before event handlers

To buffer user input events

To handle network requests

Question 7/10

What impact does a long-running synchronous task have on the JavaScript event loop?

Select your answer

It places additional tasks in the microtask queue

It gets automatically optimized by the V8 engine to improve performance

Blocks the call stack, preventing asynchronous callbacks from being executed

No impact, as the event loop can handle it efficiently

Question 8/10

What does the call stack do when a function is called in JavaScript?

Select your answer

It immediately executes the function and discards it

It moves the function to the global execution context

It pushes the function onto the stack, executes it, and pops it off when completed

It adds the function to the microtask queue

Question 9/10

What will be the output of the following code snippet when logged to the console?

async function fetchData() {
    return 'Data fetched';
}

const data = fetchData();
data.then(console.log);
console.log(data instanceof Promise);

Select your answer

[object Promise], false

Data fetched, false

Data fetched, true

[object Object], true

Question 10/10

Consider the following JavaScript code snippet. What will be logged to the console?

console.log('Start');

setTimeout(() => {
    console.log('Timeout');
}, 0);

Promise.resolve().then(() => {
    console.log('Promise');
});

console.log('End');

Select your answer

Start, End, Timeout, Promise

Start, Timeout, Promise, End

Start, End, Promise, Timeout

Start, Promise, End, Timeout

Your Results

You did not answer any questions correctly.

Your Answers

Question 1/10

😊 Your answer was correct 🙁 Your answer was incorrect

Which of the following statements about `setImmediate` in Node.js is true?

Available answers

`setImmediate` schedules a function to be executed with zero delay

`setImmediate` runs before promise handlers in the microtask queue

`setImmediate` is an alias for `setTimeout(function, 0)`

`setImmediate` executes code in the next iteration of the event loop

In Node.js, `setImmediate` is designed to execute a specified function at the end of the current event loop cycle, after I/O events, but before any `setTimeout` or event queue handlers unless specifically delayed. It is not equivalent to `setTimeout(function, 0)`, which schedules the callback within the event loop but after completing all other tasks already queued.

Question 2/10

😊 Your answer was correct 🙁 Your answer was incorrect

What is the primary role of the JavaScript event loop in the browser?

Available answers

Managing synchronous code execution

Compiling JavaScript code into machine code

Handling asynchronous operations and executing callback functions

Managing static variable declarations

The event loop in JavaScript is responsible for handling asynchronous operations. It continuously checks if the call stack is empty and if there are any callbacks waiting in the queue to be executed. When the call stack is empty, it dequeues a callback and places it in the call stack to execute it. This is essential for non-blocking code execution.

Question 3/10

😊 Your answer was correct 🙁 Your answer was incorrect

What will the following code output to the console? Assume a Node.js environment.

console.log('First');

setTimeout(() => {
    console.log('Timeout');
}, 0);

setImmediate(() => {
    console.log('Immediate');
});

process.nextTick(() => {
    console.log('Next Tick');
});

console.log('Last');

Available answers

First, Last, Next Tick, Immediate, Timeout

First, Last, Immediate, Next Tick, Timeout

First, Next Tick, Last, Immediate, Timeout

First, Last, Timeout, Immediate, Next Tick

The correct order is 'First', 'Last', 'Next Tick', 'Immediate', 'Timeout'. In Node.js, `process.nextTick()` callbacks are processed after the current operation and before any I/O tasks or timers, which explains why 'Next Tick' runs after 'Last'. Then, `setImmediate` can be invoked before `setTimeout` even if both are scheduled at zero delay.

Question 4/10

😊 Your answer was correct 🙁 Your answer was incorrect

How does JavaScript handle I/O operations like reading files with respect to the event loop?

Available answers

Using asynchronous callbacks that the event loop will execute when operations complete

Automatically converting them to synchronous operations

Queueing I/O operations in the microtask queue

By blocking the call stack until the operation completes

JavaScript, especially in environments like Node.js, handles I/O operations asynchronously. When an I/O operation is initiated, a callback is registered, and the call stack continues to execute other code without blocking. Once the I/O operation completes, the callback is placed in the event queue to be executed by the event loop.

Question 5/10

😊 Your answer was correct 🙁 Your answer was incorrect

Which of the following best describes event delegation in JavaScript?

Available answers

Directly binding events to each individual element

Attaching an event listener to a common ancestor to handle events via propagation

Capturing all event listeners in a single callback and dispatching manually

Using `setTimeout` to handle asynchronous events

Event delegation involves adding a single event listener to a common ancestor instead of individual elements. By taking advantage of event propagation (bubbling), the event listener can handle events triggered on child elements. This improves performance and simplifies code maintenance.

Question 6/10

😊 Your answer was correct 🙁 Your answer was incorrect

In the JavaScript event loop model, what is the main purpose of the microtask queue?

Available answers

To manage long-running tasks

To execute tasks immediately after the current operation completes, but before event handlers

To buffer user input events

To handle network requests

The microtask queue is used to execute tasks immediately after the current operation ends, but before any subsequent events in the event queue. Promises and `process.nextTick()` in Node.js typically use this queue. This prioritization ensures that microtasks are handled as soon as possible, often used for promise resolution callbacks.

Question 7/10

😊 Your answer was correct 🙁 Your answer was incorrect

What impact does a long-running synchronous task have on the JavaScript event loop?

Available answers

It places additional tasks in the microtask queue

It gets automatically optimized by the V8 engine to improve performance

Blocks the call stack, preventing asynchronous callbacks from being executed

No impact, as the event loop can handle it efficiently

A long-running synchronous task blocks the call stack, which means no other asynchronous callbacks can be invoked until it finishes. This can lead to poor performance and a non-responsive application since the event loop cannot process any other events until the task is completed.

Question 8/10

😊 Your answer was correct 🙁 Your answer was incorrect

What does the call stack do when a function is called in JavaScript?

Available answers

It immediately executes the function and discards it

It moves the function to the global execution context

It pushes the function onto the stack, executes it, and pops it off when completed

It adds the function to the microtask queue

When a function is called, it is pushed onto the call stack. The JavaScript engine executes the function, and once it completes, it is popped off the stack. This process repeats for nested or recursive functions, following the LIFO (Last In, First Out) principle.

Question 9/10

😊 Your answer was correct 🙁 Your answer was incorrect

What will be the output of the following code snippet when logged to the console?

async function fetchData() {
    return 'Data fetched';
}

const data = fetchData();
data.then(console.log);
console.log(data instanceof Promise);

Available answers

[object Promise], false

Data fetched, false

Data fetched, true

[object Object], true

The `fetchData` function is declared as `async`, which means it always returns a promise. Thus, `data` is an instance of `Promise`, logging `true`. The `Promise` is resolved after the synchronous code, logging the resolution, which calls `console.log` with 'Data fetched'. The actual logging of the promise takes place when the `.then(console.log)` executes the callback in the microtask queue.

Question 10/10

😊 Your answer was correct 🙁 Your answer was incorrect

Consider the following JavaScript code snippet. What will be logged to the console?

console.log('Start');

setTimeout(() => {
    console.log('Timeout');
}, 0);

Promise.resolve().then(() => {
    console.log('Promise');
});

console.log('End');

Available answers

Start, End, Timeout, Promise

Start, Timeout, Promise, End

Start, End, Promise, Timeout

Start, Promise, End, Timeout

The correct order is 'Start', 'End', 'Promise', 'Timeout'. The reason is that the synchronous code runs first ('Start' and 'End' are logged). Then, the microtask (promise) queue is processed before the macrotask queue (setTimeout), so 'Promise' is logged before 'Timeout'.