Here are Top 25 multiple-choice questions (MCQs) focused on the HTML5 features and elements in JavaScript MCQs, along with their answers and explanations.
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1. What is JavaScript?
- A programming language used for creating dynamic web pages
- A style sheet language for web development
- A markup language for structuring web content
- A database management system
JavaScript is a programming language used to create dynamic and interactive features on web pages.
2. Which keyword is used to declare a variable in JavaScript?
- var
- variable
- v
- int
In JavaScript, you can use the `var` keyword to declare variables.
3. How do you write a single-line comment in JavaScript?
- // This is a comment
- <!-- This is a comment -->
- /* This is a comment */
- # This is a comment
Single-line comments in JavaScript are written using `//`.
4. What is the purpose of the `typeof` operator in JavaScript?
- It converts a value to a different data type
- It checks the type of a value
- It performs arithmetic operations
- It defines a new variable
The `typeof` operator is used to check the data type of a value.
5. Which of the following is NOT a data type in JavaScript?
- String
- Integer
- Object
- Boolean
JavaScript does not have a data type called "Integer." Instead, it uses the `Number` data type for both integers and floating-point numbers.
6. What will the following code output. `console.log(5 + '5')`?
- 10
- 55
- 25
- Error
JavaScript performs type coercion, so it converts the number 5 to a string and concatenates it with '5'.
7. Which function is used to display a message in a popup dialog box in JavaScript?
- alert()
- display()
- message()
- popup()
The `alert()` function is used to display a message in a popup dialog box.
8. What does the `null` value represent in JavaScript?
- An empty string
- A missing or non-existent value
- A zero value
- An undefined value
The `null` value represents a missing or non-existent value in JavaScript.
9. What does the `===` operator do in JavaScript?
- It assigns a value to a variable
- It checks for equality without type coercion
- It performs addition
- It concatenates strings
The `===` operator checks for equality without performing type coercion.
10. How do you create a function in JavaScript?
- func myFunction() {}
- function. myFunction() {}
- def myFunction() {}
- function myFunction() {}
In JavaScript, you create a function using the `function` keyword, followed by the function name and parentheses.
11. Which loop is used to iterate over the properties of an object in JavaScript?
- for loop
- while loop
- do-while loop
- for...in loop
The `for...in` loop is used to iterate over the properties of an object.
12. What is the purpose of the `return` statement in a JavaScript function?
- It defines a variable
- It repeats a loop
- It ends the function and returns a value
- It comments out code
The `return` statement ends the function and specifies a value to be returned to the caller.
13. Which of the following is true about JavaScript's "hoisting"?
- Variables are moved to the top of their scope during compilation
- Variables are only accessible within the function where they are declared
- Variables are automatically initialized to zero
- Hoisting is not a concept in JavaScript
JavaScript hoists variable declarations to the top of their scope during compilation.
14. What is the purpose of the `this` keyword in JavaScript?
- It refers to the next function to be executed
- It refers to the current function
- It refers to the object that is executing the current function
- It refers to the global object
The `this` keyword refers to the object that is executing the current function.
15. How can you add a comment that spans multiple lines in JavaScript?
- /* This is a comment */
- // This is a comment
- <!-- This is a comment -->
- # This is a comment
Multiline comments in JavaScript are enclosed in `/* */`.
16. Which built-in object in JavaScript represents the global context?
- Window
- Document
- Global
- Context
The `Window` object represents the global context in a browser environment.
17. What does the `parseFloat()` function do in JavaScript?
- It converts a string to a floating-point number
- It parses an integer
- It checks if a variable is undefined
- It rounds a number to the nearest integer
The `parseFloat()` function is used to convert a string to a floating-point number.
18. How do you add an element to the end of an array in JavaScript?
- array.add(element)
- array.append(element)
- array.push(element)
- array.concat(element)
The `push()` method is used to add an element to the end of an array.
19. Which operator is used to concatenate strings in JavaScript?
- +
- &
- +
- .
The `+` operator is used to concatenate strings in JavaScript.
20. What is the purpose of the `new` keyword in JavaScript?
- It creates a new variable
- It creates a new function
- It creates a new object
- It defines a new condition
The `new` keyword is used to create a new object.
21. Which function is used to remove the last element from an array in JavaScript?
- array.pop()
- array.shift()
- array.removeLast()
- array.splice()
The `pop()` method is used to remove the last element from an array.
22. What is the purpose of the `JSON.parse()` function in JavaScript?
- It parses a JSON string and returns an object
- It creates a new JSON string
- It converts a number to a string
- It checks for syntax errors in JavaScript code
`JSON.parse()` is used to parse a JSON string and convert it into a JavaScript object.
23. Which function is used to find the length of a string in JavaScript?
- string.len()
- string.count()
- string.length
- string.size()
The `length` property of a string is used to find its length.
24. How do you declare a constant variable in JavaScript?
- const myVar
- let myVar
- var myVar
- constant myVar
You declare a constant variable in JavaScript using the `const` keyword.
25. Which built-in object represents the browser's Document Object Model (DOM) in JavaScript?
- DOMObject
- DOMElement
- document
- DOMModel
The `document` object represents the browser's Document Object Model (DOM) in JavaScript.
