Type safe, recursive `Object.freeze`.

deepFreeze.ts

// ======
// Types.
// ======

type DeepReadonly<T> = {
    readonly [K in keyof T]: T[K] extends Record<PropertyKey, unknown> ? DeepReadonly<T[K]> : T[K];
};

// ===========================
// Helper: deep freeze object.
// ===========================

/**
 * This function accepts an array or object. It freezes
 * the incoming value and any descendants recursively.
 *
 * @template T
 * @param {T} obj
 * @returns {Readonly<T>}
 */
const deepFreeze = <T>(obj: T): DeepReadonly<T> => {
    // Valid object: YES.
    if (obj && ['function', 'object'].includes(typeof obj)) {
        // Loop through.
        Reflect.ownKeys(obj as object).forEach((key): void => {
            // Recursion.
            deepFreeze(obj[key as keyof T]);
        });
    }

    // Expose object.
    return Object.freeze(obj);
};

// Export.
export { deepFreeze };