2.1. VARIABLES2.1.1. Primitive Data Types in JavaScript2.1.1.1. Numbers2.1.1.1.1. Using Arithmetic Operators2.1.1.1.2. When a Number Is Not a Number2.1.1.2. Strings2.1.1.2.1. Modifying Strings2.1.1.2.2. Converting Numbers to Strings2.1.1.2.3. Converting Strings to Numbers2.1.1.3. Boolean2.1.1.3.1. Truthy and Falsy Values2.1.1.4. Undefined and Null2.1.2. Determining a Variable's Data Type2.2. KEYWORDS AND RESERVED WORDS2.3. TRY IT2.3.1. Lesson Requirements2.3.2. Step-by-Step