JavaScript Questions

Saurabh Gupta

Score: 🔥 27

Intermediate

Took 7 minutes

Programming Language

JavaScript

100%

Questions Attempted

10 / 10

Correct Answers

Incorrect Answers

Points Earned

🔥 10

Question 1

What is a key difference between 'async/await' and traditional Promise-based code?

'async/await' doesn't use Promises internally.
'async/await' provides a more synchronous-looking syntax for asynchronous code.
'async/await' is suitable for handling synchronous operations only.
'async/await' is significantly slower than using Promises directly.

Explanation:

'async/await' is built on top of Promises, offering a cleaner and more readable syntax. It allows you to write asynchronous code that resembles synchronous code, making it easier to understand and maintain.

Question 2

What does the 'Fetch API' return as the result of a successful network request?

The requested data directly as a JavaScript object.
An error object indicating a failed request.
A Promise that resolves to a Response object.
A callback function for handling the response.

Explanation:

The Fetch API returns a Promise. Upon successful completion of the network request, this Promise resolves with a Response object. The Response object contains information about the response, such as headers and status code, and provides methods to access the response body in various formats.

Question 3

What is the primary purpose of Promises in JavaScript?

To handle synchronous operations more efficiently.
To manage asynchronous operations and their results.
To create loops that iterate over arrays.
To define object-oriented classes.

Explanation:

Promises in JavaScript provide a way to handle the outcome of asynchronous operations, whether they succeed or fail. This helps avoid callback hell and makes asynchronous code more readable.

Question 4

What is a common practice to avoid deeply nested callbacks when working with multiple asynchronous operations?

Using nested 'try...catch' blocks extensively.
Chaining multiple '.then()' methods together.
Employing synchronous functions exclusively.
Switching to a different programming language.

Explanation:

Promise chaining provides a way to structure asynchronous code sequentially without nesting callbacks deeply. By chaining '.then()' methods, the result of one asynchronous operation is passed to the next, improving readability and maintainability.

Question 5

How does the 'bind()' method in JavaScript differ from 'call()' and 'apply()'?

bind() immediately invokes the function, while call() and apply() don't.
bind() creates a new function with a bound 'this' context, while call() and apply() invoke the function immediately.
bind() can only be used with object methods, while call() and apply() can be used with any function.
bind() doesn't modify the original function, while call() and apply() do.

Explanation:

The primary distinction lies in their execution behavior. bind() returns a new function with the context of this permanently bound, whereas call() and apply() execute the function immediately with the specified context.

Question 6

In the context of ES6 classes, what is the purpose of the 'extends' keyword?

It extends the functionality of a built-in JavaScript object like Array or String.
It defines a new static method within a class.
It's used to create an instance of a parent class.
It establishes inheritance by creating a subclass that inherits properties and methods from a superclass.

Explanation:

The 'extends' keyword allows you to create a child class that inherits characteristics from a parent class, enabling code reuse and a hierarchical structure.

Question 7

Which technique can minimize DOM reflows and repaints, leading to smoother UI updates?

Using 'innerHTML' to update large sections of the DOM
Making changes to elements with 'display: none'
Batching DOM updates and using 'requestAnimationFrame'
Frequently reading element properties like 'offsetWidth'

Explanation:

Batching updates reduces the number of layout recalculations, and using 'requestAnimationFrame' allows the browser to optimize repaints, resulting in smoother animations and UI changes.

Question 8

What is the primary role of the this keyword in JavaScript?

It refers to the current date and time.
It accesses the global scope.
It points to the object that the function is a property of, determined at function call time.
It creates a new object instance.

Explanation:

The value of this is dynamically determined when a function is called, not when it's defined. It's a frequent source of confusion for developers new to JavaScript as it behaves differently compared to many other programming languages.

Question 9

Which method allows you to move up from a child element to its direct parent in the DOM?

parentElement
parentNode
previousSibling
closest()

Explanation:

The parentElement property returns the direct parent element of the current element in the DOM tree. While parentNode serves a similar purpose, it might return a different node type in situations involving Document Fragments or XML documents.

Question 10

Which built-in JavaScript method allows you to pass an array of arguments to a function, effectively spreading them as individual arguments?

apply()
call()
bind()
spread()

Explanation:

The apply() method calls a function with a given this value and arguments provided as an array. It's used to execute a function with a different context and pass multiple arguments in array form.