Crude Google Chrome Ninchanese extension

content.js

function getImageUrl(searchTerm, callback, errorCallback) {
  var api_key = 'XXX'; // NOTE, the API is limited so you need a personal API key and Custom Search Engine ID
  var cx_key = 'XXX';  // SEE: https://github.com/hubot-scripts/hubot-google-images/issues/29#issuecomment-188960728

  var searchUrl = 'https://www.googleapis.com/customsearch/v1?q=' + encodeURIComponent(searchTerm) + '&cx='+ cx_key +'&safe=high&searchType=image&key=' + api_key

  var x = new XMLHttpRequest();
  x.open('GET', searchUrl);
  x.responseType = 'json';
  x.onload = function() {
    var response = x.response;
    if (!response || !response.items ||
        response.items.length === 0) {
      errorCallback('No response from Google Image search!');
      return;
    }

    callback(response.items);
  };
  x.onerror = function() {
    errorCallback('Network error.');
  };
  x.send();
}


document.addEventListener('keyup', function(event) {
  if( event.code == 'Enter' ) {

    var images = document.getElementsByClassName('google-image')
    for (var i = images.length - 1; i >= 0; i--) {
      images[i].parentNode.removeChild(images[i]);
    }

    setTimeout(function(){

      var answerHanzi = document.getElementById('answer-hanzi').innerText;
      var answerEnglish = document.getElementById('answer-definition').innerText
      var container = document.getElementsByClassName('english-word')[0];

      getImageUrl(answerHanzi, function(items) {
        for (var i = 4; i >= 0; i--) {
          var image = document.createElement("img");
          image.className = 'google-image';
          image.width = 150;
          image.src = items[i].image.thumbnailLink;
          container.appendChild(image);
        }
      }, function(errorMessage) { console.log(errorMessage) });

    }, 200);
  }
});

manifest.json

{
  "manifest_version": 2,

  "name": "Ninchanese Images",
  "description": "This extension shows a Google image search for each word.",
  "version": "1.0",

  "content_scripts": [
      {
        "matches": ["https://app.ninchanese.com/*"],
        "js": ["content.js"]
      }
    ],

  "browser_action": {
    "default_title": "Show Google images for guessed words!"
  },
  "permissions": [
    "https://ajax.googleapis.com/",
    "https://www.googleapis.com/"
  ]
}