Are JavaScript identifiers case-sensitive?

Which of these is an invalid identifier?

A). foo_bar

B). fooBar

C). foo-bar

D). foo$bar

Can JavaScript identifiers include spaces?

A). Yes

B). No

C). Only in ES6

D). Only in strings

What is the output of the following code: var x = 5, x = 10;

A). Syntax error

B). 5

C). 10

D). Reference error

Which identifier is valid in strict mode?

A). public

B). _public

C). 123public

D). public$

Which of the following is a valid identifier name?

A). var

B). 123abc

C). _123abc

D). #abc123

What will the following code output: var x; x = 5; var y = x;

A). undefined

B). null

C). 5

D). x

Which of the following is an invalid identifier?

A). _variable

B). var$

C). 2variable

D). variable2

What is a valid identifier in JavaScript?

A). 123abc

B). abc123

C). let

D). var

Which of the following is a valid identifier?

A). if

B). else

C). null

D). value1

What will happen if you declare a variable with the name undefined?

A). Syntax error

B). Declares a variable

C). Throws a runtime error

D). Reassigns undefined