type UserBrowserExtension = 'grammarly';
export type UserBrowserExtensionResults = UserBrowserExtension[];
type BaseOptions = {
    extensions: UserBrowserExtension[];
};
type AsyncOptions = BaseOptions & {
    async: true;
    asyncTimeoutMs: number;
};
type SyncOptions = BaseOptions & {
    async?: false;
    asyncTimeoutMs?: never;
};
type Options = BaseOptions & (SyncOptions | AsyncOptions);
/**
 * Call this to return a list (or a Promise of a list) of detected browser extensions.
 *
 * This function supports a **synchronous** and **asynchronous** mode through options. You
 * must pass a list of the browser extension names you want to target for detection.
 * Only UserBrowserExtension extensions are supported, other target names will be silently
 * ignored.
 *
 * If the async option is enabled, you must also pass a final timeout by when it
 * should stop all detection attempts and return any partially detected extensions.
 *
 * Example usage:
 * ```
 * // synchronously/immediately check for extensions
 * const extensions = sniffUserBrowserExtensions({ extensions: ['grammarly', 'requestly'] });
 * // result will be ['grammarly'] or ['grammarly','requestly'] or ['requestly'] or [];
 *
 * // asynchronously check for extensions up to 30s
 * sniffUserBrowserExtensions({
 *    extensions: ['grammarly', 'requestly'],
 *    async: true,
 *    asyncTimeoutMs: 30000,
 *  }).then(extensions => {
 *    // result will be  ['grammarly'] or ['grammarly','requestly'] or ['requestly'] or [];
 *  })
 * ```
 */
export declare function sniffUserBrowserExtensions<O extends Options>(options: O): O extends AsyncOptions ? Promise<UserBrowserExtensionResults> : UserBrowserExtensionResults;
export {};