Updated Types

Author: kingroryg

basics/types.md

@@ -16,6 +16,10 @@ The most common types are:
 
 * **Objects**: a representation of a more complex object
 
+* **null**: a variable that contains null contains no valid Number, String, Boolean, Array, or Object
+
+* **undefined**: the undefined value is obtained when you use an object property that does not exist, or a variable that has been declared, but has no value assigned to it.
+
 JavaScript is a *“loosely typed”* language, which means that you don't have to explicitly declare what type of data the variables are. You just need to use the ```var``` keyword to indicate that you are declaring a variable, and the interpreter will work out what data type you are using from the context, and use of quotes.