Can identifiers start with a digit in JavaScript?

Which is a correct identifier for a variable?

A). 9variable

B). variable-9

C). variable_9

D). variable 9

Which characters are allowed in JavaScript identifiers?

A). Letters only

B). Letters and numbers only

C). Letters, numbers, $ and _

D). Any special characters

What is a valid identifier in JavaScript?

A). 123abc

B). abc123

C). let

D). var

Which identifier is valid in strict mode?

A). public

B). _public

C). 123public

D). public$

Which of the following is a valid identifier?

A). if

B). else

C). null

D). value1

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

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

Is let a valid identifier in JavaScript?

A). Yes

B). No

C). Only in ES6

D). Only in non-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