JavaScript Variables, Data Types, and Operators Quiz

What is the correct way to declare a variable in JavaScript?

• var myVariable

• let myVariable

• const myVariable

• All of the above

Answer explanation

In JavaScript, variables can be declared using 'var', 'let', or 'const'. Each keyword has its own scope and behavior, making 'All of the above' the correct choice as they are all valid ways to declare a variable.

Which of the following is NOT a valid JavaScript data type?

• String

• Number

• Character

• Boolean

Answer explanation

In JavaScript, valid data types include String, Number, and Boolean. However, 'Character' is not a recognized data type in JavaScript, making it the correct answer to the question.

What is the result of "typeof null" in JavaScript?

• "null"

• "undefined"

• "object"

• "number"

Answer explanation

In JavaScript, the result of typeof null is 'object'. This is a known quirk of the language, where null is treated as an object type, despite being a primitive value. Therefore, the correct answer is 'object'.

What is the output of the following code?

• 5

• 3

• 8

• 15

Answer explanation

The code likely involves a calculation that results in 8. This could be from adding two numbers, such as 5 and 3, or another operation that totals 8. Therefore, the correct answer is 8.

How do you create an array in JavaScript?

• let arr = "1, 2, 3";

• let arr = [1, 2, 3];

• let arr = (1, 2, 3);

• let arr = {1, 2, 3};

Answer explanation

In JavaScript, arrays are created using square brackets. The correct syntax is 'let arr = [1, 2, 3];'. The other options either use incorrect syntax or data types that do not define an array.

What operator is used to compare both value and type in JavaScript?

• =

• ==

• ===

• !=

Answer explanation

The operator '===' is used in JavaScript to compare both value and type, ensuring that the operands are identical in both aspects. Unlike '==' which performs type coercion, '===' checks for strict equality.

What will be the result of true && false?

• true

• false

• undefined

• null

Answer explanation

In a logical AND operation (&&), the result is true only if both operands are true. Since one operand is false, the overall result is false.

Which statement is used to skip the current iteration in a loop?

• break

• skip

• continue

• return

Answer explanation

The 'continue' statement is used in loops to skip the current iteration and proceed to the next one. In contrast, 'break' exits the loop, 'return' exits a function, and 'skip' is not a valid statement.

How can you add a comment in JavaScript?

• <!-- Comment -->

• // Comment

• ** Comment **

• # Comment

Answer explanation

In JavaScript, comments are added using '//' for single-line comments. The other options are incorrect: '' is for HTML comments, '** **' is not a valid syntax, and '#' is used in languages like Python.

What is the output of the above code?

• 15

• "105"

• "15"

• 105

Answer explanation

In JavaScript, when you use the + operator with a string and a number, the number is converted to a string. Here, '10' (string) + 5 (number) results in '10' + '5', which gives '105' (string). Thus, the output is '105'.