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

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#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
    });
}