Help with Smallest common multiple

function smallestCommons(arr) {
  var val;
  arr = arr.sort(function(a, b){
    return a - b;
  for(var num=1;;num++)
  function lcm(n,a,b)
  for(var i=a;i<=b;i++)
        return false;
  return true;

I first sorted the array smallest to largest, then kept an infinite loop passing no’s from 1 to n to find the number ie.lcm of array of no’s,which will stop once the number is found, then a function to find lcm of all no’s between that array. but its not working for 1,13 and 18,23 while the logic is correct… Thanks in advance.