Add book format identifier string to the book interface

README.md

@@ -86,6 +86,7 @@ It is therefore imperative that you use [Content Security Policy (CSP)](https://
 ### The Main Interface for Books
 
 Processors for each book format return an object that implements the following interface:
+- `.type`: a string that identifies the book format.
 - `.sections`: an array of sections in the book. Each item has the following properties:
     - `.load()`: returns a string containing the URL that will be rendered. May be async.
     - `.unload()`: returns nothing. If present, can be used to free the section.

fb2.js

@@ -231,6 +231,7 @@ const dataID = 'data-foliate-id'
 
 export const makeFB2 = async blob => {
     const book = {}
+
     const doc = await parseXML(blob)
     const converter = new FB2Converter(doc)
 

view.js

@@ -83,39 +83,46 @@ export const makeBook = async file => {
         const loader = await makeDirectoryLoader(file)
         const { EPUB } = await import('./epub.js')
         book = await new EPUB(loader).init()
+        book.type = 'epub'
     }
     else if (!file.size) throw new NotFoundError('File not found')
     else if (await isZip(file)) {
         const loader = await makeZipLoader(file)
         if (isCBZ(file)) {
             const { makeComicBook } = await import('./comic-book.js')
             book = makeComicBook(loader, file)
+            book.type = 'comic-book'
         }
         else if (isFBZ(file)) {
             const { makeFB2 } = await import('./fb2.js')
             const { entries } = loader
             const entry = entries.find(entry => entry.filename.endsWith('.fb2'))
             const blob = await loader.loadBlob((entry ?? entries[0]).filename)
             book = await makeFB2(blob)
+            book.type = 'fb2'
         }
         else {
             const { EPUB } = await import('./epub.js')
             book = await new EPUB(loader).init()
+            book.type = 'epub'
         }
     }
     else if (await isPDF(file)) {
         const { makePDF } = await import('./pdf.js')
         book = await makePDF(file)
+        book.type = 'pdf'
     }
     else {
         const { isMOBI, MOBI } = await import('./mobi.js')
         if (await isMOBI(file)) {
             const fflate = await import('./vendor/fflate.js')
             book = await new MOBI({ unzlib: fflate.unzlibSync }).open(file)
+            book.type = 'mobi'
         }
         else if (isFB2(file)) {
             const { makeFB2 } = await import('./fb2.js')
             book = await makeFB2(file)
+            book.type = 'fb2'
         }
     }
     if (!book) throw new UnsupportedTypeError('File type not supported')