Object Types (Deep Dive)

This deep dive builds on basic object types with advanced patterns:

Intersections – Combine multiple types into one with all properties:

type Named = { name: string };
type Aged = { age: number };
type Person = Named & Aged;  // Has both name and age

Object Unions – Model values that could be one of several shapes:

type Shape = 
  | { kind: 'circle'; radius: number }
  | { kind: 'square'; size: number };

Use the in operator to narrow unions by checking for specific properties.

Index Signatures – Create dictionary-like objects:

type Dictionary = { [key: string]: number };

Excess Property Checks – TypeScript catches typos in fresh object literals:

const user: User = { name: "Alice", agee: 30 };  // ❌ Error: 'agee'

In this category, you'll:

By the end, you'll be comfortable with advanced object type patterns and their tradeoffs.