slider next and previous button incrementation and decrementation

slider-next-prev.md

let up = true;
let down = true;
let screenCounter = 0;
let incrementBy = 1;
let defaultTftMode = "light";
const lengthOfScreen = 4;

// direction would be up or down
function changeScreen(direction = null) {
  if (direction === "up") {
    if (up == true && screenCounter <= lengthOfScreen) {
      if (screenCounter === lengthOfScreen) {
        screenCounter = 0;
      }else{
        screenCounter += incrementBy;
      }
    } else {
      screenCounter = 0;
      up = true;
    }
  }else if(direction === "down"){
    if (down == true && screenCounter !== 0) {
      screenCounter -= incrementBy;
      if (screenCounter === 0) {
        down = false;
      }
    } else {
      screenCounter = lengthOfScreen;
      down = true;
    }
  }

  console.log('screenCounter value is', screenCounter);
}