Question

Possible Duplicate:
variable === undefined vs. typeof variable === “undefined”

Assuming that undefined has not been tampered with, are the following equivalent?

typeof a === 'undefined'

and

a === undefined

?

[The reason I ask is because the author of Parsley.js seems to love writing 'undefined' !== typeof someExpression.]

Answer 1

These two approaches are almost the same, except one: typeof won’t raise ReferenceError: a is not defined in case if a variable was not defined as a variable.

Say, typeof approach is just more fool-proof.