My Sketch

let cX = 0;

let vX = 5;

let vA = 1;

let num = 0;

function setup() {

  createCanvas(windowWidth, windowHeight);

  background(33);

  angleMode(DEGREES);

  cX = width / 2;

}

​

function draw() {

  background(33);

  fill(255,255,55);

  cX += vX;

  if(cX >= width*0.8 || cX < width*0.2)

    vX *= -1;

  let cY = height / 2;

  num += vA;

  if(num < 0 || 30 <= num)

    vA *= -1;

  let sA = num

  let eA = 360-num

  if(vX < 0){

    sA += 180;

    eA += 180;

  }

  arc(cX,cY, 200, 200, sA, eA);

}