Why does 0154 === 108? [duplicate]

Question

What's happening here and why?

document.write(0154); // === 108

Answer 1

Numbers that begin with 0 are considered octal (base-8) numbers.

base 8 [0154] = base 10 [108]

but if you had used a number that had an 8 or 9 you wouldn't have seen this problem since that neither 8 nor 9 is an octal digit.

Answer 2

0154 is octal. 1*64 + 5*8 + 4 = 108.

Answer 3

its octal number. octal=0154 & decimal is=108