Partial, Pick and Omit

Built-in utility types derive new types from existing ones: Partial<T> makes every property optional, Pick<T, K> keeps some, Omit<T, K> drops some. They keep update and input types in step with the source.

What a session covers

The tutor works through these with you, in conversation and code. A session ends when you have shown them, not when a video does.

Explain what Partial, Pick and Omit each produce from a type
Derive an input type and an update type from one source type
Spot the Partial<User> patch that lets id and createdAt change

In practice

A few lines that show Partial, Pick and Omit doing its job.

TypeScript

interface User { id: string; name: string; email: string; createdAt: Date }

type NewUser = Omit<User, "id" | "createdAt">;
type UserPatch = Partial<Pick<User, "name" | "email">>;
type UserSummary = Pick<User, "id" | "name">;

function update(id: string, patch: UserPatch) { /* ... */ }
update("7", { name: "Ada" });

The common mistake

Watch for

Using Partial<User> as the type for an update when some fields must never change. It allows id and createdAt in the patch; derive the patch from Pick first.

What to know first

Your roadmap puts these before Partial, Pick and Omit, unless you already know them.

keyof constraints

How it stays learned

Once a session shows you understand Partial, Pick and Omit, it comes back for review. Each review takes a minute and tells the memory model how well you still know it.

Day 3First recall, while it is fresh
Day 7Second, a week on
Day 18Last, when it has settled

Where it leads

Topics that build on Partial, Pick and Omit.

Mapped types

Next in the moduleMapped types →