Which of the following is an invalid identifier?

What is a valid identifier in JavaScript?

A). 123abc

B). abc123

C). let

D). var

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

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

Which of the following is a valid identifier name?

A). var

B). 123abc

C). _123abc

D). #abc123

Are JavaScript identifiers case-sensitive?

A). Yes

B). No

C). Only in ES6

D). Only in strict mode

Which is a correct identifier for a variable?

A). 9variable

B). variable-9

C). variable_9

D). variable 9

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

A). Syntax error

B). 5

C). 10

D). Reference error

Can identifiers start with a digit in JavaScript?

A). Yes

B). No

C). Only in ES5

D). Only in strict mode