Which characters are allowed in JavaScript identifiers?

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

A). Syntax error

B). 5

C). 10

D). Reference error

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

Which identifier is valid in strict mode?

A). public

B). _public

C). 123public

D). public$

Which of these is an invalid identifier?

A). foo_bar

B). fooBar

C). foo-bar

D). foo$bar

Is let a valid identifier in JavaScript?

A). Yes

B). No

C). Only in ES6

D). Only in non-strict mode

Which of the following is a valid identifier name?

A). var

B). 123abc

C). _123abc

D). #abc123

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

Can JavaScript identifiers include spaces?

A). Yes

B). No

C). Only in ES6

D). Only in strings

What is the maximum length of an identifier?

A). 255 characters

B). 31 characters

C). 64 characters

D). No limit