DEV Community

Dhilip kumar
Dhilip kumar

Posted on


IMDB rating on Mouse Hover - II

Please read Part-I here for continuity.

Step 4: Initiating listener in the DOM through content.js

/* Mouse over Event handler */
function listenToMouseover() {
  window._imdb_minWaitfBeforeExecute = undefined;
  document.body.addEventListener("mouseover", function(e) {
    var x, y;
    e = e || window.event;
    x = e.clientX;
    y = e.clientY;

    /* Avoid Recognizing words inside callout || _imdb_calloutElt => callout Element */
    var calloutPositions = typeof(window._imdb_calloutElt) !== 'undefined' ? window._imdb_calloutElt.getBoundingClientRect(): {};
    if (typeof(window._imdb_calloutElt) !== 'undefined' && x <= (calloutPositions.width + calloutPositions.left) && x >= calloutPositions.left && y <= ( + calloutPositions.height) && y >= {
    /* Debounce Start */
    _imdb_minWaitfBeforeExecute = setTimeout(findIMDB.bind(this, x, y), 250);
    /* Debounce End */

When the user clicks on the Extension we called thelistenToMouseover() function.

  • loadCssToHead appends css to head.Try this as an Exercise.(We do it here because it does not load our css when the user did not intend to activate our extension)
    Also, make sure your Element’s class Names that you set are unique and does not overlap with the Webpage’s existing class names.

  • We add an event listener formouseover on document body.

  • When the user moves the pointer, get the Mouse pointer coordinates through e.clientX and e.clientY

  • We will be opening a popup on success. We don't want our Extension to recognise texts inside the popup. So, we add the logic to avoid it.We do that by calculating the coordinates where our call out lie and dont consider it for valid text hover.

  • mouseover is an expensive event likescroll which gets fired numerous times even for a small movement. So, to avoid it we are checking if the mouse at least rests 250ms on a coordinate before we start finding the IMDb. Read about debounce in javascript here.

  • When the user is on a coordinate for more than 250ms then we try finding the IMDb throughfindIMDB() function by passing the coordinates as arguments.

Step 5: Find the text inside the hovered element

function findIMDB(x, y) {
  var element = document.elementFromPoint(x,y);
  var text = '';
  // NETFLIX Specific changes
  if (window.location.href.includes('') && element.classList.value === "bob-play-hitzone") {
    text = element.parentElement.children[2].getElementsByClassName('bob-title')[0].innerText.trim();
  } else {
    text = (element && element.innerText) ? element.innerText.trim() : '';

  /* Check if Previous text found is not equal to Current Text found and Text length less than 35 to avoid big sentences from Recognizing */
  if (text && window._imdb_finderText !== text && text.length < 35) {
    window._imdb_finderText = text;
      type: 'callAPI',
      text: text
    window._imdb_posx = x;
    window._imdb_posy = y;
    console.log("Message Sent: " , text);

document.elementFromPoint(x, y) helps us find the DOM element in the given x and y coordinates.

  • Lines 5 and 6 include changes specific to Netflix where the element variable does not give the actual text due to overlay.
  • Once we get the element we find theinnerText and store it to a variable.
  • Its unnecessary API calls that we will make if the user hovers on a long sentence, so we limit the text to 35 it can be more than 35 as it breaks for cases where the movie name is longer than 35 :P
  • If we get a text then we send a message tobackground.js using 'chrome.runtime.sendMessage' to call the API and get the response back. We can also make calls in content.js but I chose to do it in background script it wont interfere with other nw calls in tree if seen in the Chrome network waterfall.
  • Set Window variables for values of x and y for which call is made. So that we can add our popup there(_imdb_posx && _imdb_posy) on getting a response.[which we will cover shortly]

Step 6: Call IMDb API from background.js

chrome.runtime.onMessage.addListener(function(request, sender, sendResponse) {
  if (request.type == "callAPI") {
    getIMDBRating(request.text).then(function(response) {
      data = JSON.parse(response);
      if (!data.Error) {
        data.type = 'ratingResponse'
        chrome.tabs.query({active: true, currentWindow: true}, function(tabs) {
          chrome.tabs.sendMessage(tabs[0].id, data)
      } else {
        console.log('No movie Found');
    return true;

function getIMDBRating(text) {
  return new Promise(function(resolve, reject) {
    var xhttp = new XMLHttpRequest();
    xhttp.onreadystatechange = function() {
      if (this.readyState == 4 && this.status == 200) {
       return resolve(this.responseText);
    var urlParam = text.split(" ").join('+');"GET", _imdb_api_url + urlParam + _imdb_apikey, true);

We have a Message listener in background.js which gets executed on receiving a message form content.js

  • Type iscallApi which we are passing from content.js
  • ThegetIMDBRating() function makes API call and gets the response.
  • The API URL and the API key are hidden by the way. You can get one for yourself over here.
  • Send the response as a message to the tab that sent the message to background js to make a API call using chrome.tabs.query

Step 7: Loading the popup

function hasGotMessage(response, sender, sendResponse) {
  switch (response.type) {
    case 'clickResponse':
      window.sessionStorage.setItem('_imdbRaterEnabled', "1");
    case 'ratingResponse':

function loadCallout(data) {
   if (window._imdb_calloutShown) {
  /* Popup rendering Start */
  var innerComponents = getInnerComponentHTML(data);
  /* parent div start*/
  var imdbElement = document.createElement('div'); = "relative";
  imdbElement.className = "_imdbClass";
  imdbElement.innerHTML = innerComponents.absElt + innerComponents.title + innerComponents.plot +
                          innerComponents.genre + innerComponents.awards+ innerComponents.line1 + innerComponents.rottenTomatoes +
                          innerComponents.metacritic + innerComponents.readMore +'</div>';
  /* parent div end */
  var childElt = imdbElement.children[0];
  findRefinedXandYcoordinates(); = 'position: fixed;top: ' + _imdb_posy + 'px; height: ' + 250 + 'px; left: ' + _imdb_posx + 'px;display: flex;flex-direction: column;justify-content: space-around;';
  /* Render Callouts End */
  window._imdb_calloutShown = true;
  window._imdb_calloutElt = childElt;
  window.onscroll = removeCallouts;

background.js on sending the response as the message to content.js we identify the type and callloadcallout() function.

We remove the existing popup if there is any.Also on scroll we'll remove it. Identify them through the parent class name or id of your callout element.[Try implementing this as an exercise]
Pass response togetInnerComponentHTML which will put required HTML templates as strings along with placing response data in the appropriate place. Then load the element to the DOM by appending it to the body directly and making it fixed and give top and bottom same as the place where the cursor was placed at the time of making API call.

NOTE: We make it fixed and append directly to the body. Helps in avoiding overlay.

  • findRefinedXandYcoordinates() helps in calculating new coordinate if the movie name is displayed at corners. (Can be done by reducing x or y’s coordinate by the width of your popup).

If you have made it this far you should be having a working IMDb on hover Extension :)

Link for the Extension

Follow me for Interesting content in your Feed :)

Thats all Folks :)

Top comments (1)

borisimple profile image
Boris Krstić

So nice and super useful extension. Thanks for providing the code!

Visualizing Promises and Async/Await 🤓

async await

☝️ Check out this all-time classic DEV post on visualizing Promises and Async/Await 🤓