According to the ECMAScript spec the integer part of a decimal number should be either zero or start with a non-zero digit. A hexadecimal value should start with 0x.
Javascript, in the major browsers, extends EMCAScript to include octal numbers. These are determined by having a sequence of digits (from 0 to 7 inclusive) start with a zero.
Given these facts, my naive implementation of a javascript interpreter would probably parse integers a bit like this:
if first_char in [1-9] then
parse_input_as_decimal()
else if first_char is 0 then
if second_char is 'x' then
parse_input_as_hexadecimal()
else if second_char in [1-7] then
parse_input_as_octal()
else
parse_input_as_zero()
However the web browsers seem to act slightly weird in that if a number beginning with zero contains the digits 8 or 9 then it reads it as a valid decimal. This can lead to oddities, especially when using a decimal point or exponent. Some examples:
011 // is octal
0011 // is octal
019 // is decimal
0091 // is decimal
011.0 // throws an error
019.0 // is decimal
011e5 // throws an error
019e5 // is decimal
My question is why do they behave like this? Is it just some quirk of history? Or is there a good reason? Is it written in some spec somewhere? Will this ever change?
I know this is a bit arcane and few people use octals in javascript these days, but I'm curious.
