How to fade-in and fade-out an LED?

You are right, I was unnecessarily complicating things. Thanks a lot for your suggestion @DrAzzy

This is what I have got now

let ledBrightness = 0;
let ledPin = D15;
let fadeIn = false;

function fadeLED() {
 if((ledBrightness <= 0) || (ledBrightness >= 1)){
   fadeIn = !fadeIn;
 }
  
  setLedBrightness(fadeIn);

}

function setLedBrightness(fadeIn){
    if(fadeIn){
    ledBrightness += 0.01;
  }
  else {
    ledBrightness -=0.01;
  }
  
  analogWrite(ledPin, ledBrightness);
}

setInterval(fadeLED , 10);