I'm really guessing what you want it to do, but here's what I think should be the JS code:

// a click on this button runs the code below
document.querySelector("#button").addEventListener("click", function () {
  // if the button has black background color,
  if (button.style.backgroundColor == 'black') {
    // it will be changed to white, and the text color will become black
    button.style.backgroundColor = 'white';
    button.style.color = 'black';
  } else {
    // otherwise, button's background color will become black,
    // and the text color will be changed to white


  }
})