dom-2-image scroll rendering

HTML

<div id="source">
  Scroll the div below and then hit "Render"
  <div id="scrollable">
  
  </div>
</div>
<img id="screenshot"/>
<br>
<button id="button">Render</button>

CSS

#source{
  height:600px;
  width:700px;
  border:2px solid blue;
}
#scrollable{
  overflow:auto;
  height:600px;
  width:700px;
  border:2px solid yellow;
}

JavaScript

/*! dom-to-image 25-09-2016 */
!function(a){"use strict";function b(a,b){function c(a){return b.bgcolor&&(a.style.backgroundColor=b.bgcolor),b.width&&(a.style.width=b.width+"px"),b.height&&(a.style.height=b.height+"px"),b.style&&Object.keys(b.style).forEach(function(c){a.style[c]=b.style[c]}),a}return b=b||{},Promise.resolve(a).then(function(a){return h(a,b.filter,!0)}).then(i).then(j).then(c).then(function(c){return k(c,b.width||p.width(a),b.height||p.height(a))})}function c(a,b){return g(a,b||{}).then(function(b){return b.getContext("2d").getImageData(0,0,p.width(a),p.height(a)).data})}function d(a,b){return g(a,b||{}).then(function(a){return a.toDataURL()})}function e(a,b){return b=b||{},g(a,b).then(function(a){return a.toDataURL("image/jpeg",b.quality||1)})}function f(a,b){return g(a,b||{}).then(p.canvasToBlob)}function g(a,c){function d(a){var b=document.createElement("canvas");if(b.width=c.width||p.width(a),b.height=c.height||p.height(a),c.bgcolor){var d=b.getContext("2d");d.fillStyle=c.bgcolor,d.fillRect(0,0,b.width,b.height)}return b}return b(a,c).then(p.makeImage).then(p.delay(100)).then(function(b){var c=d(a);return c.getContext("2d").drawImage(b,0,0),c})}function h(a,b,c){function d(a){return a instanceof HTMLCanvasElement?p.makeImage(a.toDataURL()):a.cloneNode(!1)}function e(a,b,c){function d(a,b,c){var d=Promise.resolve();return b.forEach(function(b){d=d.then(function(){return h(b,c)}).then(function(b){b&&a.appendChild(b)})}),d}var e=a.childNodes;return 0===e.length?Promise.resolve(b):d(b,p.asArray(e),c).then(function(){return b})}function f(a,b){function c(){function c(a,b){function c(a,b){p.asArray(a).forEach(function(c){b.setProperty(c,a.getPropertyValue(c),a.getPropertyPriority(c))})}a.cssText?b.cssText=a.cssText:c(a,b)}c(window.getComputedStyle(a),b.style)}function d(){function c(c){function d(a,b,c){function d(a){var b=a.getPropertyValue("content");return a.cssText+" content: "+b+";"}function e(a){function b(b){return b+":...