<div id="codeBox">
 <div id="qrDiv" style="display: none;"></div>
 <div id="qrcode"></div> 
</div>

var user_id="" //用户ID
user_id=getQueryString('user_id'); //获取user_id参数
var url= '' //请求url
  $(function(){
  //生成二维码
  var downUrl=url+user_id;
  var qrcode = new QRCode("qrDiv", {
    text: utf16to8(Url),
    render: "canvas", //渲染方式有table方式（IE兼容）和canvas方式
    width: 128,
    height: 128,
    typeNumber:-1,//计算模式
    colorDark : "#000000",   //前景色
    colorLight : "#ffffff",   //背景色
    correctLevel : QRCode.CorrectLevel.H   //容错级别
  });
  var mycanvas1=document.getElementsByTagName('canvas')[0];
  //将转换后的img标签插入到html中 
  var img=convertCanvasToImage(mycanvas1); 
   $('#qrcode').append(img);//imagQrDiv表示你要插入的容器id    
  })

  //从 canvas 提取图片 image 
  function convertCanvasToImage(canvas) { 
  //新Image对象，可以理解为DOM 
  var image = new Image(); 
  // canvas.toDataURL 返回的是一串Base64编码的URL，当然,浏览器自己肯定支持 
    // 指定格式 PNG 
  image.src = canvas.toDataURL("image/png"); 
    return image; 
  } 

  //获取请求参数值
  function getQueryString(name) {
  var reg = new RegExp('(^|&)' + name + '=([^&]*)(&|$)', 'i');
  var r = window.location.search.substr(1).match(reg);
  if (r != null) {
    return unescape(r[2]);
  }
  return null; 
   }

  //中文编码格式转换
  function utf16to8(str) {
    var out, i, len, c;
    out = "";
    len = str.length;
    for (i = 0; i < len; i++) {
      c = str.charCodeAt(i);
      if ((c >= 0x0001) && (c <= 0x007F)) {
        out += str.charAt(i);
      } else if (c > 0x07FF) {
        out += String.fromCharCode(0xE0 | ((c  12) & 0x0F));
        out += String.fromCharCode(0x80 | ((c  6) & 0x3F));
        out += String.fromCharCode(0x80 | ((c  0) & 0x3F));
      } else {
        out += String.fromCharCode(0xC0 | ((c  6) & 0x1F));
        out += String.fromCharCode(0x80 | ((c  0) & 0x3F));
      }
    }
    return out;
  }