Is This Variable Number or String?

Sometimes you have a variable in Javascript and do not know whether it is a number or a string. You can test the type of a variable by using the typeof() operator like this:

   Var x     = 1.234;
   Var y     = "Hello";
   Var Type1 = typeof(x); 
   Var Type2 = typeof(y);  
 
   Alert(Type1 + " and " + Type2);

This code displays the message "number and string".

There are six possible values that typeof returns: "number," "string," "boolean," "object," "function," and "undefined." The most useful are "number", "string" and "undefined".

 "undefined" is useful because it tells you that something does not exist yet (ie: it's undefined) so sometimes you see code like this:

   if (typeof(objGlobal.CustomerNumber) = "undefined")) objGlobal.CustomerNumber = "12345";