使用PDF.js渲染canvas实现预览pdf的效果示例

作者:袖梨 2025-07-10

一、PDF.js的下载

从官网直接下载即可,地址:http://mozilla.github.io/pdf.js/getting_started/#download

建议下载稳定版本,如下图所示:

下载完成后将压缩包解压放在项目下,按照正常引入方式引入即可。

二、使用PDF.js

1.vue使用

第一步安装:

npm install --save pdfjs-dist

第二步引入:

import PDFJS from 'pdfjs-dist'

第三步就是在页面使用即可,下面演示export default中的代码:

export default { data () {  return {   pdfDoc: null,   pageNum: 1,   pageRendering: false,   pageNumPending: null,   scale: 0.9  } }, methods: {  showPDF (url) {   let _this = this   PDFJS.getDocument(url).then(function (pdf) {    _this.pdfDoc = pdf    _this.renderPage(1)   })  },  renderPage (num) {   this.pageRendering = true   let _this = this   this.pdfDoc.getPage(num).then(function (page) {    var viewport = page.getViewport(_this.scale)    let canvas = document.getElementById('the-canvas')    canvas.height = viewport.height    canvas.width = viewport.width    // Render PDF page into canvas context    var renderContext = {     canvasContext: canvas.getContext('2d'),     viewport: viewport    }    var renderTask = page.render(renderContext)      // Wait for rendering to finish    renderTask.promise.then(function () {     _this.pageRendering = false     if (_this.pageNumPending !== null) {      // New page rendering is pending      this.renderPage(_this.pageNumPending)      _this.pageNumPending = null     }    })   })  },  queueRenderPage (num) {   if (this.pageRendering) {    this.pageNumPending = num   } else {    this.renderPage(num)   }  },  onPrevPage () {   if (this.pageNum <= 1) {    return   }   this.pageNum--   this.queueRenderPage(this.pageNum)  },  onNextPage () {   if (this.pageNum >= this.pdfDoc.numPages) {    return   }   this.pageNum++   this.queueRenderPage(this.pageNum)  } }}

2.HTML(5)使用

第一步正常下载后解压放入项目中;

第二步在项目的页面引入即可,项目结构如下图:

由于是公司项目,我将项目名遮住,大家自行取名即可,我在此处将PDF.js放入了js目录下,大家也可以直接放在项目的根目录下。

引入如下代码:

<script type='text/javascript' src='js/PDF.js/build/pdf.js'></script>

第三步即可在js中使用。

① 引入单页的pdf:

var url = sessionStorage.sencondExperience_filePath;pdfjsLib.workerSrc = 'PDF.js/build/pdf.worker.js';pdfjsLib.getDocument(url).then(function getPdfHelloWorld(pdf) {pdf.getPage(1).then(function getPageHelloWorld(page) {var scale = 1;var viewport = page.getViewport(scale);var canvas = document.getElementById('the-canvas');var context = canvas.getContext('2d');canvas.height = viewport.height;canvas.width = viewport.width;var renderContext = {canvasContext: context,viewport: viewport};page.render(renderContext);});});

需要注意的是pdfjsLib.workerSrc中,如果换成是PDFJS.workerSrc会报错:PDFJS is notdefined。有博客说在其之前加上PDFJS.disableWorker = true;会避免出错,但我尝试了错误依然存在。使用pdfjsLib.workerSrc不会出错!!!

②引入多页的pdf:

方法一:在html中设置好pdf页数对应的canvas,然后使用js一页一页的去渲染canvas。

html:

<canvas id="the-canvas01"></canvas><canvas id="the-canvas02"></canvas><canvas id="the-canvas03"></canvas>

js:

var url = sessionStorage.third_filePath;pdfjsLib.workerSrc = 'PDF.js/build/pdf.worker.js';pdfjsLib.getDocument(url).then(function getPdfHelloWorld(pdf) {pdf.getPage(1).then(function getPageHelloWorld(page) {var scale = 1;var viewport = page.getViewport(scale);var canvas = document.getElementById('the-canvas01');var context = canvas.getContext('2d');canvas.height = viewport.height;canvas.width = viewport.width;var renderContext = {canvasContext: context,viewport: viewport};page.render(renderContext);});pdf.getPage(2).then(function getPageHelloWorld(page) {var scale = 1;var viewport = page.getViewport(scale);var canvas = document.getElementById('the-canvas02');var context = canvas.getContext('2d');canvas.height = viewport.height;canvas.width = viewport.width;var renderContext = {canvasContext: context,viewport: viewport};page.render(renderContext);});pdf.getPage(3).then(function getPageHelloWorld(page) {var scale = 1;var viewport = page.getViewport(scale);var canvas = document.getElementById('the-canvas03');var context = canvas.getContext('2d');canvas.height = viewport.height;canvas.width = viewport.width;var renderContext = {canvasContext: context,viewport: viewport};page.render(renderContext);});});

可想而知,这种方法对于页面较少的pdfHIA比较合适,但是若是页数很多或者是不知道pdf的页数的情况,这种方法显然不适合了,由此推荐方法二。

方法二:只需要定义好在需要渲染的位置,再根据pdf的页数去动态渲染canvas。

html

< div id="canvas"></ div>

js

//PDF转成图片var url = sessionStorage.other_filePath;pdfjsLib.workerSrc = 'PDF.js/build/pdf.worker.js';//创建function createPdfContainer(id, className) {    var pdfContainer = document.getElementById('canvas');    var canvasNew = document.createElement('canvas');    $("canvas").on("click",function() {var url = sessionStorage.other_filePath;window.open(url);    })    canvasNew.id = id;    canvasNew.className = className;    pdfContainer.appendChild(canvasNew);};//渲染pdf//建议给定pdf宽度function renderPDF(pdf, i, id) {    pdf.getPage(i).then(function (page) {        var scale = 0.62;        var viewport = page.getViewport(scale);        //        //  准备用于渲染的 canvas 元素        //        var canvas = document.getElementById(id);        var context = canvas.getContext('2d');        canvas.height = viewport.height;        canvas.width = document.documentElement.clientWidth;        //        // 将 PDF 页面渲染到 canvas 上下文中        //        var renderContext = {            canvasContext: context,            viewport: viewport        };        page.render(renderContext);    });};//创建和pdf页数等同的canvas数function createSeriesCanvas(num, template) {    var id = '';    for (var j = 1; j <= num; j++) {        id = template + j;        createPdfContainer(id, 'pdfClass');    }}//读取pdf文件,并加载到页面中function loadPDF(fileURL) {    pdfjsLib.getDocument(fileURL).then(function (pdf) {        //用 promise 获取页面        var id = '';        var idTemplate = 'cw-pdf-';        var pageNum = pdf.numPages;        //根据页码创建画布        createSeriesCanvas(pageNum, idTemplate);        //将pdf渲染到画布上去        for (var i = 1; i <= pageNum; i++) {            id = idTemplate + i;            renderPDF(pdf, i, id);        }    });}loadPDF(url)

三、报错

1.Uncaught TypeError: Cannot read property ‘getContext’ of null

这个错误是因为在html中需要先写好<canvas>标签,定义好id,不能使用div或其他标签。

在html中:

<canvas id="my-canvas"></canvas>

2.Uncaught (in promise) UnknownErrorException {name: “UnknownErrorException”, message: “Failed to fetch”, details: “UnknownErrorException: Failed to fetch”}

这个意思是未能捕获未知错误。我在此处出错的原因主要是后台给的pdf路径有问题导致的,换一个正确的即可~~

3.Uncaught (in promise) InvalidPDFException {name: “InvalidPDFException”, message: “Invalid PDF structure”}

这个意思是说无效的PDF格式的结构,其实就是代码中渲染pdf时的结构出现错误导致的,我是因为直接对pdf的页数:pdf.numPages循环,再去渲染在canvas导致出错。错误代码如下:

for(const i in pdf.numPages){pdf.getPage(i).then(function getPageHelloWorld(page) {var scale = 1;var viewport = page.getViewport(scale);var id = i > 9 ? 'the-canvas' + i : 'the-canvas0' + i;var canvas = document.getElementById(id);var context = canvas.getContext('2d');canvas.height = viewport.height;canvas.width = viewport.width;var renderContext = {canvasContext: context,viewport: viewport};page.render(renderContext);});}

此时将id打印才明白所有id都为 the-canvas15,出现这个错误主要还是js功底不够扎实导致......所以不能这样简单的循环渲染,正确的解决方法请看上面的讲解!!!

由此关于PDF.js的使用总结就到这了,有什么问题请留言撒~~

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