Qfyilyi

Google's "Report a Bug" or "Feedback Tool" lets you select an area of your browser window to create a screenshot that is submitted with your feedback about a bug.

_{Screenshot by Jason Small, posted in a duplicate question.}

How are they doing this? Google's JavaScript feedback API is loaded from here and their overview of the feedback module will demonstrate the screenshot capability.

JavaScript can read the DOM and render a fairly accurate representation of that using canvas. I have been working on a script which converts HTML into a canvas image. Decided today to make an implementation of it into sending feedbacks like you described.

The script allows you to create feedback forms which include a screenshot, created on the client's browser, along with the form. The screenshot is based on the DOM and as such may not be 100% accurate to the real representation as it does not make an actual screenshot, but builds the screenshot based on the information available on the page.

It does not require any rendering from the server, as the whole image is created on the client's browser. The HTML2Canvas script itself is still in a very experimental state, as it does not parse nearly as much of the CSS3 attributes I would want it to, nor does it have any support to load CORS images even if a proxy was available.

Still quite limited browser compatibility (not because more couldn't be supported, just haven't had time to make it more cross browser supported).

For more information, have a look at the examples here:

http://hertzen.com/experiments/jsfeedback/

edit
The html2canvas script is now available separately here and some examples here.

edit 2
Another confirmation that Google uses a very similar method (in fact, based on the documentation, the only major difference is their async method of traversing/drawing) can be found in this presentation by Elliott Sprehn from the Google Feedback team:
http://www.elliottsprehn.com/preso/fluentconf/

Your web app can now take a 'native' screenshot of the client's entire desktop using getUserMedia():

Have a look at this example:

https://www.webrtc-experiment.com/Pluginfree-Screen-Sharing/

The client will have to be using chrome (for now) and will need to enable screen capture support under chrome://flags.

As Niklas mention you can use html2canvas library to make screenshot using js browser . I will develop his answer in this point by provide example of making screenshot using this library (in this question frame):

function report() {

  let region = document.querySelector("body"); // whole screen

  html2canvas(region, {

    onrendered: function(canvas) {

      let pngUrl = canvas.toDataURL(); // png in dataURL format

      let img = document.querySelector(".screen");

      img.src = pngUrl; 



      // here you can allow user to set bug-region

      // and send it with 'pngUrl' to server

    },

  });

}

.container {

  margin-top: 10px;

  border: solid 1px black;

}

<script src="https://cdnjs.cloudflare.com/ajax/libs/html2canvas/0.4.1/html2canvas.min.js"></script>

<div>Screenshot tester</div>

<button onclick="report()">Take screenshot</button>



<div class="container">

  <img width="75%" class="screen">

</div>

In report() function in onrendered after getting image as data-uri you can show it to user and allow him to draw "bug region" by mouse and then send screenshot and region coordinates to server.

In this example async/await version was made: with nice makeScreenshot() function.