Unions and Literals

Learning TypeScript's Unions and Literals chapter covers union and literal types in TypeScript, along with how its type system can deduce more specific (narrower) types from how our code is structured:

• How union types represent values that could be one of two or more types
• Explicitly indicating union types with type annotations
• How type narrowing reduces the possible types of a value
• The difference between const variables with literal types and let variables with primitive types
• The "billion-dollar mistake" and how TypeScript handles strict null checking
• Using explicit | undefined to represent values that might not exist
• Implicit | undefined for unassigned variables
• Using type aliases to save typing long type unions repeatedly