I am working with php and javascript,I have button "Download" and on button click i am downloding "screenshot" (as html inside "wrapper div"),But i want to set "height" and "width" of downloding screenshot,How can i do this ? Here is my code

<div id="wrapper">
<h3>Lorem Ipsum dummy text</h3>
</div>


 <button onclick="generate()">Download</button> 


<script>
(function(exports) {
    function urlsToAbsolute(nodeList) {
        if (!nodeList.length) {
            return [];
        }
        var attrName = 'href';
        if (nodeList[0].__proto__ === HTMLImageElement.prototype || nodeList[0].__proto__ === HTMLScriptElement.prototype) {
            attrName = 'src';
        }
        nodeList = [].map.call(nodeList, function(el, i) {
            var attr = el.getAttribute(attrName);
            if (!attr) {
                return;
            }
            var absURL = /^(https?|data):/i.test(attr);
            if (absURL) {
                return el;
            } else {
                return el;
            }
        });
        return nodeList;
    }

    function screenshotPage() {
        var wrapper = document.getElementById('wrapper');
        html2canvas(wrapper, {
            onrendered: function(canvas) {
                canvas.toBlob(function(blob) {
                    saveAs(blob, 'myScreenshot.png');
                });
            }
        });
    }

    function addOnPageLoad_() {
        window.addEventListener('DOMContentLoaded', function(e) {
            var scrollX = document.documentElement.dataset.scrollX || 0;
            var scrollY = document.documentElement.dataset.scrollY || 0;
            window.scrollTo(scrollX, scrollY);
        });
    }

    function generate() {
        screenshotPage();
    }
    exports.screenshotPage = screenshotPage;
    exports.generate = generate;
})(window);
</script>