Downloads and views an image on Chrome App and Extension

loadImage.js

/**
 * dl an external image resource and append it as an img element into the rootEl
 *
 * @param {String}
 *    image resource's url
 * @param {Element} Optional
 *    root element to be appended an img element.
 * @param {Function} Optional
 *    callback function. 'function(imgEl){...}'
 */
function loadImage(url, rootEl, cb) {
  if (!url) {
    console.error("url is required.");
    return cb && cb(null);
  }
  if (!rootEl) rootEl = document.body;

  let xhr = new XMLHttpRequest();

  xhr.onload = function(e) {
    if (this.readyState === XMLHttpRequest.DONE) {
      if (this.status === 200) {
        let img = document.createElement('img');
        rootEl.appendChild(img);
        img.src = window.URL.createObjectURL(this.response);
        return cb && cb(img);
      }
    }
  };

  xhr.responseType = "blob";
  xhr.open('GET', url, true);
  xhr.send();
}