Reflection Overview

TL;DR

Reflection is the ability to inspect and manipulate objects dynamically at runtime — enumerating keys with Object.keys, probing membership with in or Object.hasOwn, and reading or writing properties via the Reflect API. It powers validation libraries, form builders, and serializers; the senior concern is keeping reflection-based code type-safe since it bypasses TypeScript's static guarantees.

How it works

Core APIs

• Object.keys, Object.getOwnPropertyNames
• Reflect for dynamic access
• in operator and hasOwn

const keys = Object.keys(user);
const hasId = 'id' in user;
const value = Reflect.get(user, 'name');

Use cases

• Validation libraries
• Form builders
• Serialization and deserialization

Interview prompt

• How do you keep reflection-based code safe in TypeScript?