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JavaScript Types are Dynamic Mocktest

Question - 20

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JavaScript
JavaScript Data Types
JavaScript Types are Dynamic
Mocktest

11.

What will typeof null return in JavaScript?

A). null B). undefined C). object D). number

Answer & Solution Discuss in Board

Answer & Solution

Answer: Option C

Solution:

Due to a historical bug in JavaScript, typeof null returns "object".

12.

What happens when you add a number and a string in JavaScript?

A). An error is thrown B). The number is converted to a string C). The string is converted to a number D). Both are converted to boolean

Answer & Solution Discuss in Board

Answer & Solution

Answer: Option B

Solution:

When a number is added to a string, the number is converted to a string and concatenated.

13.

What is the type of the value returned by parseFloat("3.14abc")?

A). number B). string C). NaN D). undefined

Answer & Solution Discuss in Board

Answer & Solution

Answer: Option A

Solution:

The parseFloat function returns a number parsed from the string, ignoring invalid characters that follow.

14.

Given let a = "10"; let b = 20;, what is the result of a + b?

A). 30 B). 1020 C). 30 D). NaN

Answer & Solution Discuss in Board

Answer & Solution

Answer: Option B

Solution:

The string "10" is concatenated with the number 20, resulting in the string "1020".

15.

What is the result of typeof [] in JavaScript?

A). array B). object C). list D). undefined

Answer & Solution Discuss in Board

Answer & Solution

Answer: Option B

Solution:

Arrays are considered objects in JavaScript, so typeof [] returns "object".

16.

What does the isNaN function do?

A). Checks if a value is not a number B). Converts a value to a number C). Checks if a value is a number D). Converts a value to NaN

Answer & Solution Discuss in Board

Answer & Solution

Answer: Option A

Solution:

The isNaN function determines if a value is NaN (Not-a-Number).

17.

In JavaScript, what will be the type of a variable x after x = 5 + true;?

A). number B). string C). boolean D). undefined

Answer & Solution Discuss in Board

Answer & Solution

Answer: Option A

Solution:

The true boolean is coerced to the number 1, resulting in the sum 6, which is a number.

18.

What is the type of the value returned by JSON.parse("null")?

A). null B). string C). object D). undefined

Answer & Solution Discuss in Board

Answer & Solution

Answer: Option C

Solution:

JSON.parse("null") returns null, which is considered an object type due to JavaScript's type system.

19.

What will be the result of typeof function() {} in JavaScript?

A). function B). object C). undefined D). method

Answer & Solution Discuss in Board

Answer & Solution

Answer: Option A

Solution:

The typeof operator returns "function" for function values.

20.

How can you check if a variable is an array in JavaScript?

A). typeof variable === "array" B). Array.isArray(variable) C). variable instanceof array D). variable.constructor === array

Answer & Solution Discuss in Board

Answer & Solution

Answer: Option B

Solution:

The Array.isArray method is used to check if a variable is an array.

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