Javascript eval function returning Octal value

Question

when i try "eval" function as eval ("020 * 05 + 05") it is returning 85 instead off 105. Can someone explain me why eval function behave like this? Also suggest any to overcome this problem.

Answer 1

Numeric constants that start with a zero (like "020") are interpreted as octal. That's true for C, C++, Java, Javascript, and most any other language with even a vague cosmetic relationship to C.

If for some reason you really, really need to use "eval()", and you've got these weird strings with bogus leading zeros on the numeric constants, you might try something like this:

var answer = eval(weirdString.replace(/\b0(\d+)\b/g, '$1'));

However I wish you would find a way around using "eval()" at all. (Note the comment below noting that the hack shown above will have problems with numbers containing fractional parts.)

Answer 2

Javascript treats numbers beginning with 0 as octal. You can either remove the leading 0's or use parseInt(yourNumber,10) to convert to base 10.

Answer 3

Here is a link describing how the ParseInt function works in JavaScript and hence the reason you are getting an unexpected result.

http://www.w3schools.com/jsref/jsref_parseInt.asp

Answer 4

Here's a cleaner, safer answer, assuming you've first ensured the expression doesn't have any illegal characters (in particular any lowercase z's) in it:

"blah blah arithmetic with leading 0's... 0012.0034 + 1200 - 05.0600*0 + 0"
  .replace(/\b0+\b/g, 'z')              // replace bare zeros with sentinel 
  .replace(/[1-9\.]0+/g, m => m.replace(/0/g, 'z'))       // save these too
  .replace(/0/g, '')                    // throw away the rest of the zeros
  .replace(/z/g, '0')                       // turn sentinels back to zeros

HT Adam Wolf for reminding me of the term sentinel.