Programming SVG interfaces using JavaScript

I have been trying to learn SVG and more particularly the interface-related elements. I'll like to have some help on getting handsoff with programming the web API with JavaScript. For instance the web API SVGAltGlyphElement

SVGAltGlyphElement interface represents an <altglyph> element. This interface makes it possible to implement more sophisticated and particular glyph character. More détails in the http://ift.tt/1WRvsMJ - SVG1.1(second edition) specifications document.

I need some help mainly through a JavaScript example code to showcase how the interface can be used. The interface definition is as follows:

interface SVGAltGlyphElement : SVGTextPositioningElement, SVGURIElement {
attribute DOMString format setraises(DOMException);
attribute DOMString glyphDef setraises(DOMException); };