How to create an attribute in SVG using JavaScript?

I have a script in my application that hides g elements in an SVG that have specific ID values, but this only works if the g element has a visibility attribute. However, the SVGs I'm using do not have a visibility attribute on the g elements and I'm not in control of the source. Therefore, I need to find a way to dynymically add the visibility attribute when the parent HTML page is loaded.I have a script in my application that hides g