mouseEventInput.js

var button;
function setup() {
  createCanvas(400, 400);
  background(0);
  button = createButton('click me');
  button.position(19, 19);

	//object.mousePressed(function() { yourFunction(yourInputs);});
  button.mousePressed(function() {makeCircle(random(0,400),random(0,400));});
}

function draw(){
 makeCircle(200,200);
}

function changeBG() {
  var val = random(255);
  background(val);
}

function makeCircle(x,y) {
  ellipse(x,y, 50,50);
}