4. Static Types, Interfaces & Type Aliases

Core TypeScript Types

- Primitives: string, number, boolean - Special: void (functions returning nothing), any (disables type checking - avoid!), unknown (type-safe any)

Union & Literal Types

// Literal union type: only these 3 strings are allowed!
type BrowserName = "chromium" | "firefox" | "webkit";
// Union type:
type LocatorTarget = string | number;

Interfaces vs Type Aliases

In automation frameworks, we use interfaces for object shapes (test configs, page models):

interface TestConfig {
  baseUrl: string;
  timeout?: number;        // Optional property (indicated by ?)
  readonly retries: number; // Cannot be reassigned after creation
}

Type Assertions (as)

When you know more about a value's type than TypeScript does:

const responseData = (rawJson as { token: string }).token;