關于this.book
?showEpub?()?{
??????//?生成Book
??????this.book?=?new?Epub(DOWNLOAD_URL)
??????//?生成Rendition,通過Book.renderTo
??????//?this.book.renderTo('read')
??????console.log(this)
??????console.log(this.book)
????}
老師，這個this.book我理解的是book是data,但是在data里面并沒有定義book,為什么可以直接this.book這樣使用呢
