Object.defineProperty(<some parameters...>)

// Define the extend function
Object.defineProperty(Element.prototype, 'extend', { value: function(namespace, object) {
    // Create  the namespace and make sure on invocation the Element is bound
    Object.defineProperty(Element.prototype, namespace, { value: function() {
        var extended = Element.prototype[namespace].extended;
        for (var e in extended) {
            extended[e] = extended[e].bind(this);
        }
        return extended;
    }});

    this[namespace].extended = object;
    return this;
}});

// Extend the Element prototype with an attr function in
// the namespace 'namespace' or ofcourse whatever function
Element.prototype.extend('namespace',{
    attr: function(name, value) {
        if(arguments.length === 1) {
            return this.getAttribute(name);
        } else {
            this.setAttribute(name, value);
            return this;
        }
    }
});

document.querySelector('.a-css-class').namespace().attr('class')
// returns 'a-css-class'