07 — Objects & Interfaces

Core Concepts

• Object types — inline { key: Type } syntax
• Interfaces — named object type declarations
• Optional properties — key?: Type
• Readonly properties — readonly key: Type
• Index signatures — [key: string]: Type for dynamic keys
• Extending interfaces — interface B extends A
• Interface merging — declaring the same interface twice merges them
• Excess property checking — TS catches extra properties on object literals

Best Practices

• Use interfaces for object shapes you'll extend or implement
• Prefer readonly for properties that shouldn't change after creation
• Use index signatures sparingly — prefer Record<K, V> or Map
• Mark as many properties optional or readonly as truthfully possible