Javascript 0 in beginning of number
Solution 1
Leading 0
on a numerical literal indicates that an octal integer is the intention, unless the second digit is 8
or 9
. In that case, the leading 0
is ignored.
Because octal numeric literals must be integers, 02.5
is erroneous.
This behavior was logged as a bug in Firefox in 2014, but because there's so much JavaScript code in the world and so much of it (probably inadvertently) relies on 09.3
not being a syntax error, the bug was marked "WONTFIX".
As pointed out in a comment below, in "strict" mode octal constants are disallowed entirely.
Solution 2
A leading zero indicates an octal (base 8) number (as opposed to a decimal - base 10 - number).
A leading 0x indicates a hexadecimal number, and a leading 0b a binary number.
Therefore 09.3 defaults to decimal because the digit '9' doesn't exist in octal notation.
Edit (credit Evan Trimboli, below): 02.5 throws an exception because octal literals must be integers.
Gor
Updated on June 06, 2022Comments
-
Gor almost 2 years
I just want to understand js logic with 0-s in beginning of number. For example
var x = 09.3 // here x == 9.3 // other example 09.3 == 9.3 // returns true // but check this one var x = 02.5 // Uncaught SyntaxError: Unexpected number // or this one 02.5 == 2.5 // same error here
Can anyone explain, how it works, why in first example it works, and ignores leading zeros, but in second example it gives me a SyntaxError
Thank you