How to take screenshot of a div with JavaScript?

Question

I am building something called the \"HTML Quiz\". It\'s completely ran on JavaScript and it\'s pretty cool.

At the end, a results box pops up that says \"Your Result

Answer 1

You can't take a screen-shot: it would be an irresponsible security risk to let you do so. However, you can:

• Do things server-side and generate an image
• Draw something similar to a Canvas and render that to an image (in a browser that supports it)
• Use some other drawing library to draw directly to the image (slow, but would work on any browser)

Answer 2

If you wish to have "Save as" dialog, just pass image into php script, which adds appropriate headers

Example "all-in-one" script script.php

<?php if(isset($_GET['image'])):
    $image = $_GET['image'];

    if(preg_match('#^data:image/(.*);base64,(.*)$#s', $image, $match)){
        $base64 = $match[2];
        $imageBody = base64_decode($base64);
        $imageFormat = $match[1];

        header('Content-type: application/octet-stream');
        header("Pragma: public");
        header("Expires: 0");
        header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
        header("Cache-Control: private", false); // required for certain browsers
        header("Content-Disposition: attachment; filename=\"file.".$imageFormat."\";" ); //png is default for toDataURL
        header("Content-Transfer-Encoding: binary");
        header("Content-Length: ".strlen($imageBody));
        echo $imageBody;
    }
    exit();
endif;?>

<script type='text/javascript' src='http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js?ver=1.7.2'></script>
<canvas id="canvas" width="300" height="150"></canvas>
<button id="btn">Save</button>
<script>
    $(document).ready(function(){
        var canvas = document.getElementById('canvas');
        var oCtx = canvas.getContext("2d");
        oCtx.beginPath();
        oCtx.moveTo(0,0);
        oCtx.lineTo(300,150);
        oCtx.stroke();

        $('#btn').on('click', function(){
            // opens dialog but location doesnt change due to SaveAs Dialog
            document.location.href = '/script.php?image=' + canvas.toDataURL();
        });
    });
</script>

Answer 3

<script src="/assets/backend/js/html2canvas.min.js"></script>


<script>
    $("#download").on('click', function(){
        html2canvas($("#printform"), {
            onrendered: function (canvas) {
                var url = canvas.toDataURL();

                var triggerDownload = $("<a>").attr("href", url).attr("download", getNowFormatDate()+"电子签名详细信息.jpeg").appendTo("body");
                triggerDownload[0].click();
                triggerDownload.remove();
            }
        });
    })
</script>

quotation

Answer 4

As far as I know you can't do that, I may be wrong. However I'd do this with php, generate a JPEG using php standard functions and then display the image, should not be a very hard job, however depends on how flashy the contents of the DIV are

Answer 5

As far as I know its not possible with javascript.

What you can do for every result create a screenshot, save it somewhere and point the user when clicked on save result. (I guess no of result is only 10 so not a big deal to create 10 jpeg image of results)

Answer 6

After hours of research, I finally found a solution to take a screenshot of an element, even if the origin-clean FLAG is set (to prevent XSS), that´s why you can even capture for example Google Maps (in my case). I wrote a universal function to get a screenshot. The only thing you need in addition is the html2canvas library (https://html2canvas.hertzen.com/).

Example:

getScreenshotOfElement($("div#toBeCaptured").get(0), 0, 0, 100, 100, function(data) {
    // in the data variable there is the base64 image
    // exmaple for displaying the image in an <img>
    $("img#captured").attr("src", "data:image/png;base64,"+data);
});

Keep in mind console.log() and alert() won´t generate output if the size of the image is great.

Function:

function getScreenshotOfElement(element, posX, posY, width, height, callback) {
    html2canvas(element, {
        onrendered: function (canvas) {
            var context = canvas.getContext('2d');
            var imageData = context.getImageData(posX, posY, width, height).data;
            var outputCanvas = document.createElement('canvas');
            var outputContext = outputCanvas.getContext('2d');
            outputCanvas.width = width;
            outputCanvas.height = height;

            var idata = outputContext.createImageData(width, height);
            idata.data.set(imageData);
            outputContext.putImageData(idata, 0, 0);
            callback(outputCanvas.toDataURL().replace("data:image/png;base64,", ""));
        },
        width: width,
        height: height,
        useCORS: true,
        taintTest: false,
        allowTaint: false
    });
}