Here is my Sitecore tree

[![enter image description here](https://i.stack.imgur.com/w6ddX.png)](https://i.stack.imgur.com/w6ddX.png)

Here is my data item in the experience editor (using the default `Welcome` component). I removed the Sitecore background image that was in the CSS.

[![enter image description here](https://i.stack.imgur.com/llHoX.png)](https://i.stack.imgur.com/llHoX.png)

Here is what the layout API returns if I hit the url <http://my-first-jss-app/sitecore/api/layout/render/jss?item=/test2&sc_apikey=xxx> 

[![enter image description here](https://i.stack.imgur.com/DAUIG.png)](https://i.stack.imgur.com/DAUIG.png)

We see that into my main placeholder there is some blocks named `code` around my `Welcome` component. It seems to be code from Sitecore experience editor...

Then when I run my app I got my component but also this strange code on my page.

[![enter image description here](https://i.stack.imgur.com/cQ0eu.png)](https://i.stack.imgur.com/cQ0eu.png)

Do you know where this is come from ? Please tell me if you need more informations.