What is a valid identifier in JavaScript?

Which of these is an invalid identifier?

A). foo_bar

B). fooBar

C). foo-bar

D). foo$bar

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

A). undefined

B). null

C). 5

D). x

Can an identifier be a single character?

A). Yes

B). No

C). Only in ES5

D). Only in ES6

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

Can identifiers start with a digit in JavaScript?

A). Yes

B). No

C). Only in ES5

D). Only in strict mode

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 is a correct identifier for a variable?

A). 9variable

B). variable-9

C). variable_9

D). variable 9

Which of the following is a valid identifier name?

A). var

B). 123abc

C). _123abc

D). #abc123