Can identifiers start with a digit in JavaScript?

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

A). undefined

B). null

C). 5

D). x

Is let a valid identifier in JavaScript?

A). Yes

B). No

C). Only in ES6

D). Only in non-strict mode

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

What is the maximum length of an identifier?

A). 255 characters

B). 31 characters

C). 64 characters

D). No limit

Which of these is an invalid identifier?

A). foo_bar

B). fooBar

C). foo-bar

D). foo$bar

Are JavaScript identifiers case-sensitive?

A). Yes

B). No

C). Only in ES6

D). Only in strict mode

What does the following code do: var $ = 5;

A). Throws an error

B). Creates a variable named $

C). Creates a variable named var

D). None of the above

What is a valid identifier in JavaScript?

A). 123abc

B). abc123

C). let

D). var

Which is a correct identifier for a variable?

A). 9variable

B). variable-9

C). variable_9

D). variable 9

Which of the following is an invalid identifier?

A). _variable

B). var$

C). 2variable

D). variable2