ePub 渲染測試this.book是否生成？console.log(this.book)，沒有container對象, 也沒有： package對象，是什么原因？謝謝

<script>import?Epub?from?'epubjs'const?DOWNLOAD_URL?=?'@/assets/2018_Book_AgileProcessesInSoftwareEngine.epub'
export?default?{??name:?'Ebook',??methods:?{????//?電子書的解析與渲染????
????showEpub()?{??????
????//?生成Book對象??????
????????this.book?=?new?Epub(DOWNLOAD_URL)??????
????console.log(this.book)????}??
},??
mounted()?{????
????this.showEpub()??
?}
?}</script>
?
}
</script>