前端PDF文件转图片方法

第一步：先下载pdfjs，网址：PDF下载地址，再引入到项目中，我是标签直接引用的

第二步：html代码添加两行代码，一个是canvas用来绘图，一个是img用来最后展示转换后的pdf图片

第三步：js代码块，主要是将paf通过pdfjs插件绘制到canvas，然后再转换为QQ号卖号地图base64格式的图片

//url参数是pdf地址，imgUrl是最后的base64格式图片
showPdf(url) {
let _this = this;
let imgArr = [];
pdfjsLib.workerSrc = 'pdf.worker.js';
let loadingTask = pdfjsLib.getDocument(url);
loadingTask.promise.then(function(pdf) {
console.log('PDF loaded');
let pageNum = pdf.numPages;
// console.log(pageNum);
for (let i=1; i<=pageNum; i++) {
pdf.getPage(i).then(function(page) {
console.log('Page loaded');

let scale = 1;
let viewport = page.getViewport(scale);

// let canvas = document.getElementById('the-canvas');
let canvas = document.createElement("canvas");
let context = canvas.getContext('2d');
canvas.height = viewport.height;
canvas.width = viewport.width;

let renderContext = {
canvasContext: context,
viewport: viewport
};
let renderTask = page.render(renderContext);
renderTask.then(function () {
console.log('Page rendered');
let imgUrl = canvas.toDataURL('image/jpeg'); //转换为base64
if (imgUrl) {
imgArr[i-1] = imgUrl;
}
//pdf全部画完结束后操作
if (imgArr.length==pageNum&&!isEmpty(imgArr)) {
// let canvas2 = document.createElement("canvas");
let canvas2 = document.getElementById('the-canvas');
let context2 = canvas2.getContext('2d');
canvas2.height = viewport.height*pageNum;
canvas2.width = viewport.width;
let count = 0;
for (let j=0; j<imgArr.length; j++) {
let IMG = new Image();
IMG.src=imgArr[j];
IMG.width = viewport.width;
IMG.height = viewport.height;
IMG.onload = function () {
context2.drawImage(IMG,0,viewport.height*j);
count++;//确保所有img渲染结束后操作
if (count==pageNum) {
let canvas = document.getElementById('the-canvas');
//赋值给img
_this.imgUrl = canvas.toDataURL('image/jpeg');
}
}
}
}
});
});
}
}, function (reason) {
console.error(reason);
});

function isEmpty(arr) {
for(let i=0;i<arr.length;i++) {
if(!arr[i])
return true;
}
return false;
}
}

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