In order to do follow this steps:
Open Atelier -> Go to "Help" -> "Install New Software"
Select the repository All available sites
Click "Next" -> "Next" -> Accept the Terms of the License Agreement -> "Finish"
Wait for the software to install, then restart Atelier (by clicking "Yes" button at pop up window)
Right-click on .html or .js file -> "Open With" -> "Other..."
Select "Internal editors"
If you like it, you can make it as the default one easily.
Let me share some screenshots to see a brief of what you get:
So you go from this (in Explorer):
And of course you will have a richer outlier window plus syntax, etc...