super-simple svg feature detection

gistfile1.html

<script>
  function addClass(el, cl) {
    el.className += ' ' + cl;
  }
 
  function supportsSVG() {
    return !!document.createElementNS && !!document.createElementNS('http://www.w3.org/2000/svg', "svg").createSVGRect;
  }
 
  if(supportsSVG) {
    console.log(document.querySelectorAll("body"));
    addClass(document.querySelectorAll("body")[0], "svg");
  }
 
</script>