jspdf的使用，js 根据base64字符串生成pdf

<script src="https://cdn.bootcss.com/html2canvas/0.5.0-beta4/html2canvas.js"></script>
<script src="https://cdn.bootcss.com/jspdf/1.3.4/jspdf.debug.js"></script>

img.onload = function(){
　　//使用h5画布重新画出返回的base64图片，直接写进pdf会失真和不完整，估计是格式有问题
    let can = $('<canvas width="' + img.naturalWidth+'" height="'+ img.naturalHeight
        +'"></canvas>').get(0);
    can.getContext("2d").drawImage(img,0,0);
    let canvasBase64 = can.toDataURL('image/jpeg',2.0);
    var pdf = new jspdf('p', 'pt', 'a4');
//l:横向， p：纵向
　　//var doc = new jsPDF('p', 'mm', [290, 210]);
    var contentWidth = can.width;
    var contentHeight = can.height;

    //一页pdf显示html页面生成的canvas高度;
    //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;
　　//x位置，y位置，宽，高
    pdf.addImage(canvasBase64, 'jpeg', 0, 0, 592.28,  592.28/contentWidth * contentHeight);
    pdf.save('test.pdf');
};