Empty vs. undefined, more about Booleans (#13)

* Use Crockford terminology: "Vars which are not explicitly initialized are given the value undefined." https://www.crockford.com/javascript/survey.html

* Change casing of Boolean reserved words. Add section for Boolean NOT operator.

Author: paulinetheitgirl

js/level1.js

@@ -64,8 +64,11 @@
     var variableName;
 
     So, we created a variable named variableName, but it has no information or
-    value inside. It is empty. To give our variable a value (initialize it)
-    use the '=' sign:
+    value inside. It is undefined. 
+
+    console.log("variableName is", variableName);
+    
+    To give our variable a value (initialize it) use the '=' sign:
 
     variableName = 'Hello world!';
 
@@ -80,10 +83,10 @@
     Strings - set of characters, word(s), or phrases that we wrap in quotes, like
               'hello world!'
     Numbers - either integers or floats(decimals). Not wrapped in quotes
-    Boolean - it represents logical values - True or False
+    Boolean - it represents logical values - true or false.
 */
 
-// TODO: Now create two empty variables named numberOne and numberTwo.
+// TODO: Now create two undefined variables named numberOne and numberTwo.
 
 
 
@@ -314,6 +317,20 @@
 
 
 
+/* 
+    Boolean Operators
+    =================
+    Putting an exclamation (!) before a Boolean variable gives 
+    the opposite value. The ! is called a "not" operator when 
+    used this way.
+
+    // the result of a comparison is a Boolean value, so we can
+    // save it to a variable
+    var bool = (1 < 2); 
+    console.log(bool); 
+    console.log(!bool); // "not true", therefore false
+    console.log(bool); // the original value isn't affected
+*/
 
 ///////////////////////////////////////////////////////////////////////////
 // Congratulations! You have finished Part 1 of JavaScript Basics!       //