Function passing parameters

Question

Here is a small JavaScript. I'm getting unexpected results from the function. 020*2 gives 32 instead of 40. Does anybody know how to fix this??

function myFunction(a, b) {
  return a * b;
}

document.write('04 * 03 = ');
document.write(myFunction(04, 03)); //Result 12, correct
document.write('  <<  Correct <br/>020 * 02 = ');
document.write(myFunction(020, 02)); //Result 32, wrong - expected result 40
document.write('  <<  Expected 40 here');

This is because a number that starts with 0 is treated as octal: http://stackoverflow.com/questions/12888075/javascript-alert-number-starting-with-0 — Jonathan.Brink, Apr 03 '15 at 14:50
@Jonathan.Brink Any number that starts with a zero and doesn't have any 8 or 9s in it. `08 == 8` — Ruan Mendes, Apr 03 '15 at 14:57

Mr. Polywhirl · Answer 1 · 2015-04-03T14:58:05.177

6

020 octal => 16 decimal
02 octal => 2 decimal

16 * 2 = 32.

Example

Convert the octal value to a base 8 (octal) string and then parse it in base 10 (decimal).

var x = 020;                                                  // 16 (octal)
var y = 02;                                                   // 2  (octal)

document.body.innerHTML = x + ' x ' + y + ' = ' + x * y;      // 32

document.body.innerHTML += '<br />';                          // {Separator}

var x2 = parseInt(x.toString(8), 10);                         // 20 (decimal)
var y2 = parseInt(y.toString(8), 10);                         // 2  (decimal)

document.body.innerHTML += x2 + ' x ' + y2 + ' = ' + x2 * y2; // 40

edited Apr 03 '15 at 14:58

answered Apr 03 '15 at 14:51

Mr. Polywhirl

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What is the purpose of this? What use will octals provide? `08 === 010 //true!?` – KJ Price Apr 03 '15 at 14:52
@KJPrice 08 is not an octal. It's treated as a decimal. It's the same use as hexadecimals :) – Ruan Mendes Apr 03 '15 at 14:56

Moishe Lipsker · Answer 2 · 2015-04-03T15:00:58.943

As mentioned in the comments, putting a zero before the number will change its type from decimal (1 - 10) to octal (1 - 8). To keep the numbers decimal, remove the leading zeros.

Here is your code with this suggestion:

function myFunction(a, b) {
    return a * b;
}

document.write('04 * 03 = ');
document.write(myFunction(4, 3));     //Result 12, correct
document.write('  <<  Correct <br/>20 * 2 = ');
document.write(myFunction(20, 2));     //Result 40, correct
document.write('  <<  Correct ')

The reason why myFunction(04, 03) works correctly is because it has no numbers in the eight spot. On the other hand 20 * 02 has a 2 in the eight spot in 20 that is interpreted as 2 times eight or 16 when it is multiplied by an octal 02.

Function passing parameters

2 Answers2

Example