adding Text to SVG document in javascript

I think you need to create a text node to hold the string and append that to the SVG text element.

var svgNS = "http://www.w3.org/2000/svg";
var newText = document.createElementNS(svgNS,"text");
newText.setAttributeNS(null,"x",x);     
newText.setAttributeNS(null,"y",y); 
newText.setAttributeNS(null,"font-size","100");

var textNode = document.createTextNode(val);
newText.appendChild(textNode);
document.getElementById("g").appendChild(newText);

There's a working example at http://old.carto.net/papers/svg/manipulating_svg_with_dom_ecmascript/.

var txt = document.createElementNS(svgNS, 'text');
txt.setAttributeNS(null, 'x', x);
txt.setAttributeNS(null, 'y', y);
txt.setAttributeNS(null,'font-size','100');
txt.innerHTML = val;
document.getElementById("g").appendChild(txt);