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 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.