Graphics buffer: trying to "fade out" an uint8array / best (fastest) way to manipulate pixels

Thanks Gordon! mapInPlace sure is much faster. Here's my fade code with callback:

function fade(b, direction, callback) {
  var m = 1;
  var clone = new Uint8Array(b.length);
  clone.set(b);
  var interval = setInterval(function () {
    if(direction===0){
      E.mapInPlace(b, clone, function (x) {
        return x * m;
      });
    }else{
      E.mapInPlace(b, clone, function (x) {
        return x - (x * m);
      });
    }
    
    m *= direction===0?0.85:0.95;
    leds.buffer = clone;
    leds.flip();
    if (m <= (direction===0?0.01:0.1)) {
      clearInterval(interval);
      if (callback) {
        callback();
      }
      E.mapInPlace(b, clone, function (x) {
        return direction===0?0:x;
      });
      leds.buffer = clone;
      leds.flip();
    }
  }, 10);
}