Почему num undefined?

function getNum() { 
  var content = prompt('Enter number:'); 
  var result = cnvertNum(content); 
  console.log(result); 
  if (result == true) { 
    return content; 
  } else { 
    getNum(); 
  } 
} 
 
function cnvertNum(content) { 
  var int = parseInt(content); 
  if (!isNaN(int)) { 
    return true; 
  } else { 
    return false; 
  } 
} 
 
var num = getNum(); 
console.log(num);