i recently started on a node project and two of the modules i\'m using is express and EJS. but default i usually use eclipse as my IDE, it works well for java and decent for htm
For me, the best way has been:
Windows > Preferences > General > Content types
In window Content types i've selected Text > HTML
and window File associations click Add... and i've included *.ejs
For a specific file, try right-click, Open With -> Other... -> HTML editor. You can also set the file association globally under Window -> Preferences -> General -> Editors -> File Associations.
On a Mac, the global setting is under Mac Option -> Preferences and all the same options.
As an addendum to rlegendi's answer, if you'd also like the proper html coloring, you need to go to "Content Types" (right above "Editors" in the Preferences). From here, select Text -> HTML and click on "Add..", including .ejs