in sim/visuals/buttons.ts [16:27]
public init(bus: EventBus, state: CommonButtonState, svgEl: SVGSVGElement, otherParams: Map<string>) {
this.state = state;
this.bus = bus;
this.defs = [];
this.element = this.mkBtn();
let pinStr = pxsim.readPin(otherParams["button"]);
this.pinId = pxsim.pinIds[pinStr];
this.button = new CommonButton(this.pinId);
this.state.buttonsByPin[this.pinId] = this.button;
this.updateState();
this.attachEvents();
}