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

I have got it to work(sort of), but I am not happy with it. It feels like there is/should be a better way to do it than below.

While googling I found this jhonny-five example, which is quite nice. https://github.com/rwaldron/johnny-five/blob/master/docs/led-fade.md

A LED class might make it easier for a beginner like me to start with Espruino. In all, loving Espruino so far. Need to learn Javascript to fully appreciate it though.

/* This example works by dividing 1 second into 10 ms time intervals and increasing/decreasing the led's analogWrite output by .01 per interval, to produce the fade-in and fade-out effects.
*/

var ledPower =0;
var ledPin = D15;

function fadeIn(callback){
  //start fadeIn effect should take 1 second to finish.
    var result = setInterval(function(){
      analogWrite(ledPin, ledPower);
      ledPower+= 0.01;
       if(ledPower >= 1){
        clearInterval(result);
        return;
      }
  }, 10);
  
  //set the fade-out effect to start after 1 second.
  setTimeout(callback, 1000);
}

function fadeOut(){
    var result = setInterval(function(){
      analogWrite(ledPin, ledPower);
      ledPower-= 0.01;
       if(ledPower <= 0){
        clearInterval(result);
        return;
      }
  }, 10);
}


setInterval(function(){
  fadeIn(fadeOut);
} , 2000);