var w = $("#code").width();  
var h = $("#code").height();//要将 canvas 的宽高设置成容器宽高的 2 倍  
var canvas = document.createElement("canvas");  
    canvas.width = w * 2;  
    canvas.height = h * 2;  
    canvas.style.width = w + "px";  
    canvas.style.height = h + "px";  
var context = canvas.getContext("2d");//然后将画布缩放，将图像放大两倍画到画布上  
    context.scale(2,2);  
    html2canvas(document.querySelector("#code"), {          
canvas: canvas,         
 onrendered: function(canvas) 
{                ...        
  }    
});  

<section class="share_popup" id="html2canvas">  
<p>html2canvas 的使用非常简单，简单到只需要传入一个 DOM 元素，然后通过回调拿到 canvas</p>  
<p><img src="1.jpg"></p>  
<p>html2canvas 的使用非常简单，简单到只需要传入一个 DOM 元素，然后通过回调拿到 canvas</p>  
 </section>

var str = $('#html2canvas');  
//console.log(str);  
html2canvas([str.get(0)], {  
    onrendered: function (canvas) {  
        var image = canvas.toDataURL("image/png");  
        var pHtml = "<img src="+image+" />";  
        $('#html2canvas').html(pHtml);  
    }  
});