export declare function isImage(extension: string): boolean;
export declare function isPdf(extension: string): boolean;
export declare function isWordDoc(extension: string): boolean;
export declare function isText(extension: string): boolean;
export declare function isExcelDoc(extension: string): boolean;
export declare function isPowerPointDoc(extension: string): boolean;
/**
 * Gets the extension of the file (without the dot '.').
 * Throws an exception if the file is undefined.
 * @param file the file
 * @returns the extension of the file.
 */
export declare function extensionOf(file: File | Blob): string;