How to use xFade?

I am following this tutorial to concat two videos with a transition in between but I can't find a way to set the flag for xfade

`https://github.com/ffmpegwasm/ffmpeg.wasm/blob/master/examples/browser/concatDemuxer.html `

Here's the snippet of my code thus far -

```
await ffmpeg.run( "-f", "concat", "xfade=transition=fade:duration=1:offset=3", "-safe", "0", "-i", "concat_list.txt", "output.mp4");
const data = await ffmpeg.FS("readFile", "output.mp4");
```

And the error that I get is this -

`Uncaught (in promise) Error: ffmpeg.FS('readFile', 'output.mp4') error. Check if the path exists`

Is it possible to set xfade parameters in ffmpeg.wasm? If so then how?