Record & Readonly

Intermediate~18 min

Record creates object types with specific keys and values, while Readonly makes all properties immutable.

Record & Readonly Types

Output

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Utility Types:

Record<K, T> - Create object with keys K and values T
Readonly<T> - Make all properties read-only

When to Use

Utility	Use Case	Example
Record	Maps, dictionaries	`Record<string, number>`
Readonly	Immutable config	`Readonly<Config>`

Common Mistakes

1. Readonly is Shallow

interface User {
    settings: { theme: string };
}

type ReadonlyUser = Readonly;

let user: ReadonlyUser = { settings: { theme: "dark" } };
// user.settings = {};  // ✗ Error - readonly
user.settings.theme = "light";  // ✓ OK - nested not readonly!

Best Practice: Use Record for maps/dictionaries, Readonly for configuration objects.

Summary

Record<K, T> creates typed object maps
Readonly<T> makes properties immutable
Perfect for dictionaries and config
Readonly is shallow - doesn't affect nested objects

What's Next?

Congratulations! Module 5 complete. Next: Type Manipulation!

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