$.mouse

let keyState = "";

if($.mouse.leftDown) {
    keyState = "Left button down";
}
else if($.mouse.rightDown) {
    keyState = "Right button down";
}
else if($.mouse.wheel.up) {
    keyState = "Mouse wheel up";
}
else if($.mouse.wheel.down) {
    keyState = "Mouse wheel down";
}
else {
    keyState = "Press a mouse button";
}

$.text.print($.w/2, $.h/2, keyState);