/**
 * Inject a JS or CSS asset into the document, resolving once it loads.
 *
 * Results are memoized by file URL so the same asset is injected only once.
 *
 * @param file - The URL of the asset to inject; its extension selects the type.
 * @param id - The element id to assign; defaults to a generated unique id.
 * @returns A promise resolving when the asset loads and rejecting on failure
 *   or on an unsupported extension.
 * @example
 * await injectAsset('https://example.com/widget.js')
 */
export declare const injectAsset: ((file: string, id?: any) => Promise<unknown>) & import('lodash').MemoizedFunction;
/**
 * Inject several assets in parallel, resolving once all have settled.
 *
 * A failed asset still counts as settled so one broken URL cannot leave the
 * batch promise pending forever.
 *
 * @param args - Asset URLs, either as separate arguments or nested arrays.
 * @returns A promise resolving when every asset has loaded or failed.
 * @example
 * await injectAssets('a.js', 'b.css')
 */
export declare const injectAssets: (...args: string[]) => Promise<void>;