JAVASCRIPT

p5js left mouse click

if (mouseButton === LEFT) { // LEFT MOUSE BUTTON
  //do stuff...
}
else if (mouseButton === RIGHT) { // RIGHT MOUSE BUTTON
  //do other stuff...
}
else if (mouseButton === CENTER) { // MOUSE WHEEL
  //do other stuff...
}

p5js right mouse button released

var rightPressed = false;

function mouseClicked() {
    if(mouseButton === RIGHT) {
        rightPressed = true;
    }
}