Object shapes

Record

Builds an object type from a key set and one value type.

What it is

The constructor to `Pick`’s selector. Given a union of keys and a value type it produces the object with those keys, and given `string` it produces an index signature instead. Those two behaviours look similar and are not: one is a fixed shape and the other is a dictionary.

Examples

```
Record<'a' | 'b', number>
```
→{ a: number; b: number; }
```
Record<string, number>
```
→{ [x: string]: number; }
An index signature, not a fixed shape — every key is allowed and none is guaranteed.
```
Record<'id', string>
```
→{ id: string; }

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

What it does not do

It does not promise the keys exist at run time. `Record<string, number>` will happily let you read a key that was never set, and hand you `number` for it.
It does not vary the value per key. When each key needs its own value type, you want a mapped type with `as`, not `Record`.

Takeaway

A literal union of keys gives you a shape the compiler will check. `string` gives you a dictionary it cannot. Choose deliberately.