Snippet for amazon recommend items

AmazonRecommendItemsGetter.js

// manifest.json
/*
  ...
  "permissions": [
    "*://*.amazon.co.jp/*",
    "*://*.amazon.com/*"
    or
    "<all_urls>"
  ], 
  ...
*/

document.querySelector("#btn").onclick = function() {
  let kwd = document.querySelector("#txt").value;
  // get a recommend item
  getAmazonRecommend(kwd, 3, function(err, items) {
    if (err) {
      console.error(err);
      return;
    }
    console.log("items:", items);

    let pane = document.querySelector("#pane");
    let len = items.length;
    for (let i = 0; i < len; i++) {
      loadImage(items[i].imgsrc, pane);
    }
  });
}

document.querySelector("#btn2").onclick = function() {
  let url = document.querySelector("#txt").value;
  let rootEl = document.getElementById("pane");
  loadImage(url, rootEl, function(imgEl) {
    console.log("imgEl:", imgEl);
  });
}

/**
 * get amazon recommend items.
 * @param {String} keyword
 * @param {Integer} max item's count to get. default is 3.
 * @param {Function} callback. 'function(err, items){...})'
 */
function getAmazonRecommend(kwd, max, cb) {
  const URL_BASE = "https://www.amazon.co.jp/s/ref=nb_sb_noss_2?__mk_ja_JP=%E3%82%AB%E3%82%BF%E3%82%AB%E3%83%8A&url=search-alias%3Daps&field-keywords=";
  const TIMEOUT = 10000;
  let url = URL_BASE + encodeURIComponent(kwd);
  let xhr = new XMLHttpRequest();

  xhr.onload = function() {
    if (this.readyState === XMLHttpRequest.DONE) {
      if (this.status === 200) {
        let els = this.responseXML.querySelectorAll(".s-result-item");
        let items = makeItems(els);
        if (items.length <= 0) {
          return cb("No items recommended.");
        }
        return cb(null, items);
      } else {
        return cb(this.statusText);
      }
    }
  };

  xhr.ontimeout = function() {
    return cb("The request for ${url} timed out.");
  };

  xhr.responseType = "document";
  xhr.timeout = TIMEOUT;
  xhr.open("GET", url);
  xhr.send(null);

  function makeItems(els) {
    if (!els || els.length <= 0) return [];
    let arr = [];
    let el;
    let p, img;
    let title, href, imgsrc;
    let len = (max >= els.length) ? els.length : max;
    for (let i = 0; i < len; i++) {
      el = els[i];
      // image url
      img = el.querySelector("img");
      if (img) {
        imgsrc = img.src;
      }
      // title
      p = el.querySelector(".a-link-normal[title]");
      if (!p) continue;
      title = p.title;
      // link
      href = p.href;
      if (!title || !href) {
        continue;
      }
      //
      arr.push({
        title,
        href,
        imgsrc,
      });
    }
    return arr;
  }
}