TypeScript 4.3: Template String Types

TypeScript 4.3 turns the type system into a programming language itself.

Template Literal Types

You can now concatenate types!

type Color = "red" | "blue";
type Quantity = "one" | "two";

type Item = `${Color}-${Quantity}`;
// Item is "red-one" | "red-two" | "blue-one" | "blue-two"

This is incredibly useful for typing strings that follow a specific pattern, like CSS classes or Event names.