前端实现pdf在线预览功能

项目需求要实现在线预览pdf文件功能，PDF区别于office的三类文档在于它不会默认打开链接自动下载而是浏览。PDF文件理论上可以在浏览器直接打开预览但是需要打开新页面。如果对预览页面UI有要求的情况下可以直接通过canvasc画布来实现。

安装依赖：npm install pdfjs-dist 我安装的是@2.0.943版本

下面是实现的完整代码：

HTML：

<template>
  <div class="pdf-wrapper">
    <canvas v-for="page in pages" :id="'the-canvas' + page" :key="page"></canvas>
  </div>
</template>

JS：

import PDFJS from 'pdfjs-dist'
PDFJS.GlobalWorkerOptions.workerSrc = '../../node_modules/pdfjs-dist/build/pdf.worker.min.js'
export default {
  data() {
    return {
      pdfDoc: null,
      pages: 0  // 页码
    }
  },
  methods: {
    loadFile(url) {
      let that = this
      PDFJS.getDocument(url).then(function (pdf) {
        that.pdfDoc = pdf
        that.pages = that.pdfDoc.numPages
        that.$nextTick(() => {
          that.renderPage(1)
        })
      })
    },
    renderPage(num) {
      let _this = this
      _this.pdfDoc.getPage(num).then(function (page) {
        let canvas = document.getElementById('the-canvas' + num)
        let ctx = canvas.getContext('2d')
        let dpr = window.devicePixelRatio || 1.0
        let bsr =
          ctx.webkitBackingStorePixelRatio ||
          ctx.mozBackingStorePixelRatio ||
          ctx.msBackingStorePixelRatio ||
          ctx.oBackingStorePixelRatio ||
          ctx.backingStorePixelRatio ||
          1.0
        let ratio = dpr / bsr
        let viewport = page.getViewport(window.screen.availWidth / page.getViewport(1).width)
        canvas.width = viewport.width * ratio
        canvas.height = viewport.height * ratio
        canvas.style.width = viewport.width + 'px'
        canvas.style.height = viewport.height + 'px'
        ctx.setTransform(ratio, 0, 0, ratio, 0, 0)
        var renderContext = {
          canvasContext: ctx,
          viewport: viewport
        }
        page.render(renderContext)
        if (_this.pages > num) {
          _this.renderPage(num + 1)
        }
      })
    }
  }
}