JavaScript Basics - variables, loops, arrays, functions, events, DOM interactions, alert-confirm-prompt, rollover images - One Line Questions
1.
What is the difference between `var` and `let` when declaring variables? —
`var` has function scope or global scope, `let` has block scope
2.
Consider the array `let fruits = ['apple', 'banana', 'cherry'];`. What will `fruits[1]` return? —
'banana'
3.
What is the result of `console.log(typeof 'Hello')`? —
'string'
4.
What is the output of `console.log(2 + 3 + '5')`? —
'235'
5.
What is the value of `fruits.length` for the array `let fruits = ['apple', 'banana', 'cherry'];`? —
3
6.
What is an anonymous function in JavaScript? —
A function that is not declared with a name
7.
What is an 'event' in the context of JavaScript and web development? —
A user action or system occurrence that can be detected by JavaScript
8.
In JavaScript, what is an array? —
A special type of variable that can hold multiple values under a single name
9.
What is a closure in JavaScript (related to functions)? —
A function's ability to access variables from its outer scope even after the outer function has finished executing
10.
Which statement best describes the `prompt()` function's return value when the user clicks 'Cancel'? —
null
11.
What is a 'rollover image' technique in web development? —
An image that changes when the mouse pointer hovers over it
12.
How do you add an element to the end of a JavaScript array? —
array.push(element)
13.
What is the basic syntax for accessing an element in a JavaScript array by its index? —
arrayName[index]
14.
What is the scope of a variable declared with `var` inside a function? —
Function scope
15.
Which JavaScript function displays a message box with an OK button? —
alert()
16.
Which keyword is used to declare a variable in JavaScript that can be reassigned? —
let
17.
What does the `const` keyword do in JavaScript? —
Declares a variable that cannot be reassigned
18.
The `prompt()` function in JavaScript is used to: —
Display a message and get text input from the user
19.
What does 'DOM' stand for in web development? —
Document Object Model
20.
How can you change the text content of an HTML element using JavaScript? —
All of the above
21.
To remove an HTML element using JavaScript, you can use: —
element.remove()
22.
How do you add a new attribute to an HTML element using JavaScript? —
element.setAttribute('attributeName', 'value')
23.
Which loop is guaranteed to execute at least once? —
do...while loop
24.
Which loop is commonly used for iterating over the properties of an object? —
for...in loop
25.
Which keyword is used to define a function in JavaScript? —
function
26.
Which of the following is a way to declare a function expression in JavaScript? —
const myFunction = function() {}
27.
Which DOM method is used to select all elements with a specific tag name? —
getElementsByTagName()
28.
Which DOM method is used to select an HTML element by its ID? —
getElementById()
29.
Which DOM method returns an HTMLCollection of all elements with a given class name? —
getElementsByClassName()
30.
What event occurs when the value of an input element changes and the element loses focus? —
onchange
31.
What is the event triggered when a user presses a key on the keyboard? —
onkeydown
32.
In JavaScript, a function can: —
Return any data type, including other functions
33.
Which event listener is triggered when a user clicks on an HTML element? —
onclick
34.
What is the JavaScript method to remove the last element from an array? —
pop()
35.
What does the `shift()` array method do? —
Removes the first element and returns it
36.
What is the `unshift()` array method used for? —
Adding elements to the beginning
37.
What does `document.querySelector('.my-class')` do? —
Selects the first element with the class 'my-class'
38.
Which of the following is NOT a valid JavaScript data type? —
Character
39.
What is the primary use of `alert()`, `confirm()`, and `prompt()`? —
Providing simple user interaction and feedback
40.
What is an argument in a JavaScript function? —
The actual value passed to the function when it is called
41.
What is a parameter in a JavaScript function? —
A variable listed inside the parentheses in the function definition
42.
What is the primary advantage of using `let` and `const` over `var` in modern JavaScript? —
They provide block-scoping, reducing potential errors.
43.
What is the purpose of the `confirm()` function in JavaScript? —
To display a message with OK and Cancel buttons
44.
What is the purpose of the `while` loop in JavaScript? —
To execute a block of code as long as a specified condition is true
45.
What is the primary purpose of a `for` loop in JavaScript? —
To iterate over a sequence of elements a specified number of times
46.
What is the purpose of `addEventListener()`? —
To attach an event handler to an element
47.
What is the `event.preventDefault()` method used for? —
To prevent the default action of an element (e.g., following a link)
48.
To implement a rollover image, you typically need to: —
Use JavaScript to change the `src` attribute of the `<img>` tag on mouse events
49.
Which statement about JavaScript variables is true? —
Variables declared with `var` are hoisted.
50.
Which loop is most suitable for iterating over the elements of an array when the number of iterations is known? —
for loop