https://developer.chrome.com/extensions/examples/tutorials/getstarted/popup.js fix

popup.js

// Copyright (c) 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

/**
 * Get the current URL.
 *
 * @param {function(string)} callback - called when the URL of the current tab
 *   is found.
 */
function getCurrentTabUrl(callback) {
  // Query filter to be passed to chrome.tabs.query - see
  // https://developer.chrome.com/extensions/tabs#method-query
  var queryInfo = {
    active: true,
    currentWindow: true
  };

  chrome.tabs.query(queryInfo, function(tabs) {
    // chrome.tabs.query invokes the callback with a list of tabs that match the
    // query. When the popup is opened, there is certainly a window and at least
    // one tab, so we can safely assume that |tabs| is a non-empty array.
    // A window can only have one active tab at a time, so the array consists of
    // exactly one tab.
    var tab = tabs[0];

    // A tab is a plain object that provides information about the tab.
    // See https://developer.chrome.com/extensions/tabs#type-Tab
    var url = tab.url;

    // tab.url is only available if the "activeTab" permission is declared.
    // If you want to see the URL of other tabs (e.g. after removing active:true
    // from |queryInfo|), then the "tabs" permission is required to see their
    // "url" properties.
    console.assert(typeof url == 'string', 'tab.url should be a string');

    callback(url);
  });

  // Most methods of the Chrome extension APIs are asynchronous. This means that
  // you CANNOT do something like this:
  //
  // var url;
  // chrome.tabs.query(queryInfo, function(tabs) {
  //   url = tabs[0].url;
  // });
  // alert(url); // Shows "undefined", because chrome.tabs.query is async.
}

/**
 * @param {string} searchTerm - Search term for Google Image search.
 * @param {function(string,number,number)} callback - Called when an image has
 *   been found. The callback gets the URL, width and height of the image.
 * @param {function(string)} errorCallback - Called when the image is not found.
 *   The callback gets a string that describes the failure reason.
 */
function getImageUrl(searchTerm, callback, errorCallback) {
  // Google image search - 100 searches per day.
  // https://developers.google.com/custom-search/json-api/v1/using_rest
  var cx = 'insert-your-cx-from:https://cse.google.com'
  // WARNING: Hard-coding your api key in code is really insecure
  var key = 'insert-your-key-from:https://console.developers.google.com'
  var searchUrl = 'https://www.googleapis.com/customsearch/v1?searchType=image'
    + '&cx=' + encodeURIComponent(cx)
    + '&key=' + encodeURIComponent(key)
    + '&q=' + encodeURIComponent(searchTerm);
  var x = new XMLHttpRequest();
  x.open('GET', searchUrl);
  // The Google image search API responds with JSON, so let Chrome parse it.
  x.responseType = 'json';
  x.onload = function() {
    // Parse and process the response from Google Image Search.
    var response = x.response;
    if (!response || !response.items || !response.items.length) {
        errorCallback('No response from Google Image search')
        return;
    }
    var firstResult = response.items[0];
    // Take the thumbnail instead of the full image to get an approximately
    // consistent image size.
    var imageUrl = firstResult.image.thumbnailLink;
    var width = parseInt(firstResult.image.thumbnailWidth);
    var height = parseInt(firstResult.image.thumbnailHeight);
    console.assert(
        typeof imageUrl == 'string' && !isNaN(width) && !isNaN(height),
        'Unexpected respose from the Google Image Search API!');
    callback(imageUrl, width, height);
  };
  x.onerror = function() {
    errorCallback('Network error.');
  };
  x.send();
}

function renderStatus(statusText) {
  document.getElementById('status').textContent = statusText;
}

document.addEventListener('DOMContentLoaded', function() {
  getCurrentTabUrl(function(url) {
    // Put the image URL in Google search.
    renderStatus('Performing Google Image search for ' + url);

    getImageUrl(url, function(imageUrl, width, height) {

      renderStatus('Search term: ' + url + '\n' +
          'Google image search result: ' + imageUrl);
      var imageResult = document.getElementById('image-result');
      // Explicitly set the width/height to minimize the number of reflows. For
      // a single image, this does not matter, but if you're going to embed
      // multiple external images in your page, then the absence of width/height
      // attributes causes the popup to resize multiple times.
      imageResult.width = width;
      imageResult.height = height;
      imageResult.src = imageUrl;
      imageResult.hidden = false;

    }, function(errorMessage) {
      renderStatus('Cannot display image. ' + errorMessage);
    });
  });
});