Require failing with Simple-XDM error

I am trying to require a different js file and I receive the error:
[Simple-XDM] require is not defined ReferenceError: require is not defined

I am using
“atlassian-connect-express”: “^3.0.1”,
“atlassian-connect-js”: “^5.1.62”,
Node 6.1.0

My code works on Node, but it fails when trying to run it as part of the plugin.
What is the correct way to require methods from a different js file on the same project?