size of createElement("svg") is 0,0

Solution 1:

createElement can only create HTML elements, you need createElementNS

var svg=document.createElementNS("http://www.w3.org/2000/svg", "svg");
document.body.appendChild(svg);
svg.setAttribute("class","jscreated");
svg.style.width="500px";
svg.style.height="400px";
<svg class="HTML_SVG" style="width:500px; height:400px;" class="HTML_SVG"></svg>