Essential TypeScript 5, Third Edition

7 Understanding static types

This chapter covers

• Restricting the range of types that can be as signed to variables or used in operations
• Relying on the compiler to infer types
• Using any, never, and unknown types to broaden or restrict the range of values
• Creating type unions that combine multiple types
• Using type assertions and type guards to narrow types
• Controlling how the JavaScript null and undefined values can be used

In this chapter, I introduce the key TypeScript features for working with data types. The features I describe in this chapter are the foundations for working with TypeScript, and they are the building blocks for the advanced features described in later chapters.

I start by showing how TypeScript’s types differ from pure JavaScript’s ...