Adafruit VS1053 Codec + MicroSD Breakout - MP3/WAV/MIDI/OGG Play + Record - v4

It looks like you missed out the f.close I'd suggested, so the file will be left open which will use memory?

Try:

function _playSoundFile(file)
{
  LED3.write(1);
  var filename = "/audio/" + file;
  f = E.openFile(filename,"r");
  w = undefined;
  w = new Waveform(2048, {doubleBuffer:true});
  w.buffers = [ w.buffer, w.buffer2 ];
  w.buffer.set(f.read(w.buffer.length));
  w.buffer2.set(f.read(w.buffer.length));
  var fileBuf = f.read(w.buffer.length);
  w.on("buffer", function(buf) {
    buf.set(fileBuf);
    fileBuf = f.read(buf.length);
    if (fileBuf===undefined)
    {
      _stopSoundFile();
    }
  });
  analogWrite(AUDIOUT, 0.5, {freq:20000});
  w.startOutput(AUDIOUT,8000,{repeat:true}­);
}
function _stopSoundFile()
{
  LED3.write(0);
  if (w && w.running) w.stop();
  AUDIOUT.write(0);
  w = undefined;
  if (f) f.close();
  f = undefined;
}

Another option is just to leave the w object defined... Something like below should work:

var w = new Waveform(2048, {doubleBuffer:true});
var fileBuf, f;
w.buffers = [ w.buffer, w.buffer2 ];
w.on("buffer", function(buf) {
    buf.set(fileBuf);
    fileBuf = f.read(buf.length);
    if (fileBuf===undefined)
    {
      _stopSoundFile();
    }
});

function _playSoundFile(file)
{
  LED3.write(1);
  var filename = "/audio/" + file;
  f = E.openFile(filename,"r");  
  w.buffer.set(f.read(w.buffer.length));
  w.buffer2.set(f.read(w.buffer.length));
  fileBuf = f.read(w.buffer.length); 
  analogWrite(AUDIOUT, 0.5, {freq:20000});
  w.startOutput(AUDIOUT,8000,{repeat:true}­);
}
function _stopSoundFile()
{
  LED3.write(0);
  if (w.running) w.stop();
  AUDIOUT.write(0);
  if (f) f.close();
  f = undefined;
}