错误代码：
These dependencies were not found:
* canvas in ./node_modules/pdfh5/js/pdf.js
* dommatrix/dist/dommatrix.js in ./node_modules/pdfh5/js/pdf.js
* web-streams-polyfill/dist/ponyfill.js in ./node_modules/pdfh5/js/pdf.worker.js
To install them, you can run: npm install --save canvas dommatrix/dist/dommatrix.js web-streams-polyfill/dist/ponyfill.js
解决方法：
npm install --save canvas dommatrix web-streams-polyfill
