JavaScript for Web Development: Master Client-Side Scripting

Question 1

Which of the following is the correct syntax to add an event listener to an HTML element using JavaScript?

Accepted Answer

element.addEventListener('event', function);

Answer

element.attachEvent('event', function);

Answer

element.addListener('event', function);

Answer

element.handleEvent('event', function);

Question 2

Which of the following is NOT a best practice for writing efficient JavaScript code?

Accepted Answer

Using closures excessively.

Answer

Using the strict mode.

Answer

Avoiding global variables.

Answer

Using a linter.

Question 3

Which JavaScript data type should you use to represent a logical value?

Accepted Answer

Boolean

Answer

Number

Answer

String

Answer

Object

Question 4

What does the 'use strict' directive do in JavaScript?

Accepted Answer

It enables strict mode, enforcing stricter rules.

Answer

It disables strict mode, allowing for more flexibility.

Answer

It sets the global scope to strict mode.

Answer

It does nothing.

Question 5

The purpose of the **'this'** keyword in JavaScript is to refer to:

Accepted Answer

The current object

Answer

The global object

Answer

The parent object

Answer

The child object

Question 6

Which event listener is used to detect when a user clicks an element?

Accepted Answer

onclick

Answer

onhover

Answer

onfocus

Answer

onchange

Question 7

Which of the following is **not** a best practice for writing efficient JavaScript code?

Accepted Answer

Use global variables for convenience

Answer

Use variables to store frequently used values

Answer

Cache DOM elements to avoid repeated lookups

Answer

Use event delegation to improve performance

Question 8

The purpose of the **'strict mode'** in JavaScript is to:

Accepted Answer

Enforce stricter rules for JavaScript code

Answer

Make JavaScript code more flexible

Answer

Improve the performance of JavaScript code

Answer

Provide backwards compatibility with older versions of JavaScript

Question 9

Which of the following is a way to iterate over the elements of an array in JavaScript?

Accepted Answer

for loop

Answer

foreach loop

Answer

while loop

Answer

do-while loop

Question 10

'==' checks for loose equality, while '===' checks for:

Accepted Answer

Strict equality

Answer

Loose equality

Answer

Boolean equality

Answer

Object equality

Question 11

What is a key benefit of using event delegation in JavaScript?

Accepted Answer

Enhances performance by minimizing event listeners

Answer

Simplifies code by attaching listeners to a single element

Answer

Increases memory usage by creating more listeners

Question 12

In JavaScript, which option is NOT a primitive data type?

Accepted Answer

Array

Answer

String

Answer

Number

Answer

Boolean

Question 13

What is the primary purpose of the 'addEventListener' method?

Accepted Answer

To attach an event handler to an HTML element

Answer

To remove an event handler from an HTML element

Answer

To create a new HTML element

Answer

To get the current value of an HTML element

Question 14

Explain the distinction between the 'getElementById' and 'getElementsByTagName' methods.

Accepted Answer

getElementById retrieves a single element by its unique ID, while getElementsByTagName retrieves a collection of elements by their tag name

Answer

getElementsByTagName retrieves a single element by its tag name, while getElementById retrieves a collection of elements by their ID

Answer

Both methods perform the same function

Answer

Neither of these methods are defined in JavaScript

Question 15

What is the primary objective of using 'strict mode' in JavaScript?

Accepted Answer

To enforce stricter syntax and variable declaration rules

Answer

To provide an alternative syntax for JavaScript

Answer

To enhance the speed of JavaScript code execution

Answer

To restrict the usage of specific keywords

Question 16

Which of the following options represents a valid variable name in JavaScript?

Accepted Answer

_myVariable

Answer

123

Answer

$myVariable

Answer

my-variable

Question 17

Explain the difference between 'var' and 'let' variable declarations.

Accepted Answer

var has a global or functional scope, while let has a block scope

Answer

let has a global or functional scope, while var has a block scope

Answer

Both declarations have the same scope

Answer

Neither of these declarations exist in JavaScript

Question 18

Which data structure in JavaScript allows for the representation of item collections accessible via keys?

Accepted Answer

Object

Answer

Array

Answer

Queue

Answer

Set

Question 19

What is the intended purpose of the 'console.log' method?

Accepted Answer

To display output in the console

Answer

To clear the console

Answer

To create a new variable

Answer

To obtain user input

Question 20

Which of the following is NOT a recognized event type in JavaScript?

Accepted Answer

Hover

Answer

Click

Answer

Load

Answer

Submit

Question 21

Explain the distinction between a 'function expression' and a 'function declaration'.

Accepted Answer

A function expression is anonymous, while a function declaration is named

Answer

A function declaration is anonymous, while a function expression is named

Answer

Both declarations are identical

Answer

Neither of these declarations are defined in JavaScript

Question 22

In JavaScript, which method allows you to select an element based on its class name?

Accepted Answer

getElementsByClassName

Answer

getElementsByClass

Answer

getElementByClassName

Answer

querySelectorByClass