support PDF preview

    <template>
      <div>
    <div id="the-canvas"></div>
      </div>
    </template>
    
    <script>
    import PDFJS from "pdfjs-dist";
    import { TextLayerBuilder } from "pdfjs-dist/web/pdf_viewer";
    import "pdfjs-dist/web/pdf_viewer.css";
    PDFJS.GlobalWorkerOptions.workerSrc = "pdfjs-dist/build/pdf.worker.js";
    
    export default {
      data(){
    return{
      scale: 1,
    }
      },
      mounted() {
    const parentBox = document.querySelector(`#the-canvas`);
    //为了让pdf和容器有一个内边距，所以减去了20
    this.boxWidth = parentBox.offsetWidth - 20;
    this.getPDF();
    conso