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DeepReadonly<T>

DeepReadonly<T> = T extends object ? { readonly [P in keyof T]: DeepReadonly<T[P]> } : T

Makes all properties of T readonly recursively, at every depth level.

Unlike TypeScript's built-in Readonly<T> which only affects the first level, DeepReadonly<T> makes nested object properties readonly as well.

Type Parameters​

T: T​

The type to make deeply readonly

Since​

2.0.0

Example​

type Config = {
  server: {
    host: string;
    port: number;
  };
  debug: boolean;
};

type FrozenConfig = `DeepReadonly<Config>`;
// All properties are readonly at every level

const config: FrozenConfig = { server: { host: "localhost", port: 3000 }, debug: true };
config.debug = false; // ❌ Error: Cannot assign to 'debug' because it is a read-only property
config.server.port = 8080; // ❌ Error: Cannot assign to 'port' because it is a read-only property