writing in processing vs javascript in processing.js

Question

My understanding is that Processing.js converts Processing code into javascript. But if one does not want to write in Processing, one can use methods and properties of the processing object like so:

function sketchCirc(processing) {

    function drawCirc() {
            processing.background(100);
            processing.ellipse(X,Y,radius,radius);
            processing.fill(0,121,184);
            processing.stroke(255);
        }

    processing.draw = function() {

        drawCirc();
    }

I prefer to use the above approach (meaning accessing methods of the processing object), but are there any downsides to this? I want to avoid having to learn the Processing language from scratch. Please let me know what your ideas are.