Javascript Runtime error :Object expected (on variable definition)

[immunity]

when i try to put :

var text = document.getElementById("account").value;

it popup me this error :/

 

Also this error pop up when i try

if(IsNumeric()){....}

function IsNumeric()
{
   var ValidChars = "0123456789.";
   var IsNumber=true;
   var Char;


   for (i = 0; i < document.getElementById("phone").value.length && IsNumber == true; i++) 
	  { 
	  if (ValidChars.indexOf(document.getElementById("phone").value.charAt(i)) == -1) 
		 {
		 IsNumber = false;
		 }
	  }
   return IsNumber;
   
   }

[Corona4456]

It depends on what  the element is... what's the "account" element supposed to be?