Built-in utility types, composition, readonly, record.

Utility Types — Partial, Required, Pick, Omit, and More

TypeScript built-in utility types transform existing types without duplication. Partial<T> makes all properties optional. Required<T> makes all required. Pick<T,K> extracts a subset of keys. Omit<T,K> removes keys. Readonly<T> prevents mutation. Record<K,V> constructs a mapped type. Awaited<T> unwraps Promise. These compose: Readonly<Partial<User>> makes a fully optional immutable User type.

Interactive Pipeline Flow

UnderstandImplementOptimise

📦 Source — original type

All utility types take an existing type as input and produce a transformed type. They are implemented with mapped types and conditional types internally.

Architecture Diagrams

Combining utility types for DTO patterns.

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Key Design Decisions

✂️Omit<User, "password"> beats manual type duplication

Don't write a PublicUser type manually that copies all User props minus password. Use Omit<User, 'password'>. When User gains a new property, PublicUser automatically gains it too.

📋Record over index signatures for known keys

Record<'admin'|'editor'|'viewer', Permission[]> is safer than {[key: string]: Permission[]} because it ensures all three roles are present. Index signatures allow any string key.

🔗Compose utility types like functions

Utility types compose. Readonly<Partial<T>> is a perfectly valid immutable partial type. Required<Omit<T,"secret">> removes a key and ensures the rest are required. Build from primitives.

Discussion