text: function undefValue(element_id) {
      var x;
      document.getElementById(element_id).innerHTML = x
  }
  
  function logicalExample1(element_id) {
      var x=20, y=15, t=true, f=false;
      document.getElementById(element_id).innerHTML = x > y && f
  
  }
  
  function logicalExample2(element_id) {
      var x=20, y=15, t=true, f=false;
      document.getElementById(element_id).innerHTML = x==y || t
  }
  
  function typeofExample(element_id, which_var) {
      var x,y,z;
  
      x = 10
      y = "pizza"
      z = true
  
      switch (which_var) {
          case "x":
              document.getElementById(element_id).innerHTML = typeof x;
              break;
          case "y":
              document.getElementById(element_id).innerHTML = typeof y;
              break;
          case "z":
              document.getElementById(element_id).innerHTML = typeof z;
      }
  }