网页生成图片，转PDF

    引用JS
    	<script src="js/jquery-2.1.4.js"></script>
	<script src="js/html2canvas.js"></script>
	<script src="js/jspdf.js"></script>
    Html
    <button type="button"  id="down_btn">下载PDF</button>
    <div style="width: 824px;height:1192px;text-align: center;margin: 0 auto;background:red;" id="box"></div>

    JS
    $('#sbt').click(function(){
           downpdf('box');
    })
    function dowpdf(id){
            	

            	
				const cntElem=document.getElementById(id);
					var shareContent=cntElem;
					var width=shareContent.offsetWidth;
					var height=shareContent.offsetHeight;

					var canvas=document.createElement('canvas');
					var scale=3;

					canvas.width=width*scale;
					canvas.height=height*scale;

					canvas.getContext('2d').scale(scale,scale);

					var opts={
						scale:scale,
						canvas,
						width:width,
						height:height,
						useCORS:true,
					};



					html2canvas(shareContent,opts).then(canvas=>{
						var context=canvas.getContext('2d');
						context.mozImageSmoothingEnabled=false;
						context.webkitImageSmoothingEnabled=false;
						context.msImageSmoothingEnabled=false;
						context.imageSmoothingEnabled=false;

						var dataUrl=canvas.toDataURL("image/jpeg");

						var newImg=document.createElement('img');
						newImg.src=dataUrl;
						newImg.setAttribute('id','newImg');
						newImg.style.width=canvas.width/scale+'px';
						newImg.style.height=canvas.height/scale+'px';

						// document.getElementById('box2').appendChild(newImg);

						var contentWidth = canvas.width;
						var contentHeight = canvas.height;
						
						//一页pdf显示html页面生成的canvas高度;
						var pageHeight = contentWidth / 592.28 * 841.89;
						//未生成pdf的html页面高度
						var leftHeight = contentHeight;
						//页面偏移
						var position = 0;
						//a4纸的尺寸[595.28,841.89]，html页面生成的canvas在pdf中图片的宽高
						var imgWidth = 595.28;
						var imgHeight = 592.28/contentWidth * contentHeight;
		

						var url= canvas.toDataURL("image/jpeg");
						
						var image = new Image();
						image.src = canvas.toDataURL("image/jpeg");
						
						
						var doc = new jsPDF('','pt','a4');
						// PDF分页
						image.onload = function() {
		                    if (leftHeight < pageHeight) {
		                        doc.addImage(image.src,'jpeg',0,0,imgWidth,imgHeight );
		                    } else {
	                            while(leftHeight > 0) {
	                                doc.addImage(image.src, 'jpeg', 0, position, imgWidth, imgHeight)
	                                leftHeight -= pageHeight;
	                                position -= 841.89;
	                                if(leftHeight > 0) {
	                                    doc.addPage();
	                                }
	                            }
	                        }
	                        doc.save("名称.pdf");
	                    }
						;					
                    });

            }