Returning 0 makes perfect sense. parseInt matches an integer from the beginning of the string, so it reads the 0 and then stops at the 8 because 8 is not a vali

Returning 0 makes perfect sense. parseInt matches an integer from the beginning of the string, so it reads the 0 and then stops at the 8 because 8 is not a valid digit in base 8. >>> parseInt("123foobar", 10) 123