Decimal to binary recursive function in JavaScript

Question

I wanted to write a recursive function in js to calc the binary represenation of a decimal number.

I did manage to solve this by :

var t = (function f(n, s)
{
    return((s = (n % 2) + s) && (n == 0)) ? s : f(Math.floor(n / 2), s);
})(4, '');

console.log(t);

Fiddle: http://jsbin.com/ihezev/3/edit

However, I can't get rid of the leading zero.

So if I execute the IIFE with 7 it yields : 0111 and I want 111.

How can I get rid of the leading 0?

(without string replace solution please. I want to keep it as much elegant as I can.. and I know I can do alert(Number(234).toString(2)) but this question is tagged as recursion.)

philosophercode · Accepted Answer · 2021-01-02T08:19:13.377

4

Here's a clean one I ported from python

const decToBi = num => num === 0 ? 0 : num % 2 + 10 * decToBi(Math.floor(num / 2));
console.log(decToBi(10)); //1010

edited Jan 02 '21 at 08:19

answered Jan 25 '19 at 23:54

philosophercode

56
4

Why is the number 1253343 not converted correctly with this function ? – jmtalarn Feb 12 '21 at 10:55

score 2 · Answer 2 · answered Jan 18 '13 at 12:28

2

A little bit changed but still elegant:

var t = (function f(n, s) {
    return n === 0 ? s || "0" : f(~~(n / 2), (n % 2) + s);
})(7, "");  // "111"

answered Jan 18 '13 at 12:28

VisioN

143,310
32
282
281

@RoyiNamir It can be even more elegant if we omit parenthesis `n % 2 + s` :) – VisioN Jan 18 '13 at 12:38
@RoyiNamir This is a [shortcut](http://stackoverflow.com/questions/5971645/what-is-the-double-tilde-operator-in-javascript) for `Math.floor`. – VisioN Jan 18 '13 at 13:20

score 2 · Answer 3 · answered Mar 15 '21 at 15:55

2

function base10ToString(num, str = "") {
  if (num === 0) {
    return str;
  }
  if (num % 2 === 0) str = "0" + str;
  else str = "1" + str;
  return base10ToString(Math.floor(num / 2), str);
}
console.log(base10ToString(7));

answered Mar 15 '21 at 15:55

Sebastian Pajes

21
1

score 0 · Answer 4 · answered Jan 18 '13 at 12:05

0

You'll need to pass a parameter which represents whether you've produced a 1 yet. Whilst that parameter is false, you don't produce anything for a 0.

answered Jan 18 '13 at 12:05

Oliver Charlesworth

267,707
33
569
680

score 0 · Answer 5 · answered Aug 03 '22 at 02:57

0

function binaryConversion(num) {
    if (num === 0) {
        return "";
    }
    return binaryConversion(Math.floor(num / 2)) + (num % 2).toString();
}

answered Aug 03 '22 at 02:57

Francisco Henrique Oliveira

1

Decimal to binary recursive function in JavaScript

5 Answers5