Object shapes

Pick

Keeps only the named keys, and checks that they exist.

What it is

A mapped type over `K` rather than over `keyof T`, which is why the result is a plain object rather than a copy of the original. The constraint `K extends keyof T` is doing real work: pick a key that is not there and the error arrives at the type, not later at a property access.

Examples

```
Pick<{ a: string; b: number }, 'a'>
```
→{ a: string; }

Pick<{ a: string; b: number; c: boolean }, 'a' | 'c'>

→{ a: string; c: boolean; }

```
Pick<{ readonly a: string }, 'a'>
```
→{ readonly a: string; }
`readonly` is carried across, because `Pick` maps over a key set derived from `T`.

Each resolved type above was printed by TypeScript 5.9.3, not written by hand.

What it does not do

It does not accept keys that are missing. That is a feature, and it is the difference between `Pick` and `Omit` — the latter accepts anything.
It does not distribute over a union in `T`. `Pick<A | B, K>` picks from the union as one thing rather than from each member.

Takeaway

When you want a subset and you want to be told about typos, `Pick` is the one with the guard rail.