LayoutTests/svg/custom/js-late-clipPath-creation.svg

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1 Basic//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11-basic.dtd">  
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"  id="svg-root" width="100%" height="100%" viewBox="0 0 480 360" onload="createClipPath()">
<g id="content" transform="scale(1, 1.5)">
     <text font-size="60" fill="navy" clip-path="url(#dynClip)" x="10" y="70">Clipped. INVISIBLE.</text>
</g>
<script>
    var content = document.getElementById("content");

    function createClipPath()
    {
        var clipPath = document.createElementNS("http://www.w3.org/2000/svg", "clipPath");
        clipPath.setAttribute("id", "dynClip");
        clipPath.setAttribute("clipPathUnits", "userSpaceOnUse");

        var path = document.createElementNS("http://www.w3.org/2000/svg", "path");
        path.setAttribute("d", "M 0 0 l 200 0 l 0 200 l -200 0 Z");

        clipPath.appendChild(path);
        content.appendChild(clipPath);
    }
</script>

</svg>