tostring - JavaScript Detecting Octal Value at Different Scenario -

var x = 02345;    var y = x.tostring();      alert(y);

i realized there problem converting leading zeroes number string in javascript using tostring() method.

as can see output of code above, output 1253 instead of supposedly 02345.

if leading 0 removed, code work expected, why? happening code above can change work expected.

var x = 2345;    var y = x.tostring();      alert(y);

edit : reason asked question because have 2 different codes work differently despite being similar. after reading question has nothing tostring() method, why first set of code below not detect number octal value second set of code does.

var num=window.prompt(); // num = 0012222 var str = num.tostring(); var result = [str[0]];  for(var x=1; x<str.length; x++)   {     if((str[x-1]%2 === 0)&&(str[x]%2 === 0))      {       result.push('-', str[x]);      }     else      {       result.push(str[x]);      }   } alert(result.join('')); //outputs : 0-012-2-2-2 

the other code :

function numberdash(num) {     var stringnumber = num.tostring();     var output = [stringnumber[0]];      (var = 1; < stringnumber.length; i++) {         if (stringnumber[i-1] % 2 === 0 && stringnumber[i] % 2 === 0) {             output.push('-', stringnumber[i]);         } else {             output.push(stringnumber[i]);         }     }     return output.join(''); }   numberdash(0012222) // outputs : "52-6-6"; 

many javascript engines add octal numeric literals specification. leading 0 indicates octal (base 8). 2345 in base 8 (octal) 1253 in base 10 (decimal):

 octal  decimal -----  -------------------- 2      2 * 8 * 8 * 8 = 1024  3     3 * 8 * 8 =      192   4    4 * 8 =           32    5                      5 -----  -------------------- 2345                   1253 

you can disable using strict mode. see §b.1.1 of specification. doing makes 02345 syntax error.

so it's nothing tostring, it's 02345 in code isn't value expect.

---

re updated question:

why first set of code below not detect number octal value second set of code does

because in first code, you're not dealing number, you're dealing string. window.prompt returns string, not number, if type in digits.

even if converted string number via number(num) or +num, rules runtime string->number conversion different rules parsing javascript source code.