Как перевернуть число? [требует правки]

var num = 5921; 
 
function getReversedNum(num) { 
  let result = 0; 
  while (num) { 
    result = result * 10 + num % 10; 
    num = Math.floor(num / 10); 
  } 
 
  return result; 
} 
 
console.log(getReversedNum(num));

function reverseInt(number) { 
  var result = ''; 
   
  while(number>0){ 
   result = result + (number%10); 
   number = parseInt(number/10); 
  } 
   
  return result; 
} 
 
var number = 5921; 
console.log(reverseInt(number));

revert = num => { 
  let i = 0, result=0; 
  for(let r=1; r<num; r=10**++i) result+=(((num-num%r)/r)%10)/r; 
  return result*(10**(i-1)); 
} 
console.log([321,48735,90008].map(revert))

function reverse(num, r = 0){ 
    if(!num) return r; 
    r =  r * 10  + num % 10; 
    return reverse(Math.floor( num / 10), r); 
} 
console.log(reverse(12345));

var x = 5921; 
var y = 0; 
for(; x; x = Math.floor(x / 10)) { 
    y *= 10; 
    y += x % 10; 
} 
console.log(y);