Importing a javascript file into another in server-side code

I am using a server-side javascript engine based on Spider monkey (1.8.5) and cannot upgrade due to legacy reasons.

I have a native function exposed in javascript, let say, called load_file(filePath) which loads the contents of a file. I am creating a javascript library and want to use module-like structures in my project. I have two javascript files and I want to import one into another. I also want to use 'use strict' for security reasons.

Contents of the library (lib.js):

'use strict';
(function() {
  /* .. code .. */
  return { obj1: obj1};

Usage in the file

'use strict';
function require(filePath) {
  return eval(load_file(filePath));

  var lib = require('lib.js');
  // Usage goes like: lib.obj1

In every new javascript file I create, I have to duplicate the code for require. Moreover, I am not a fan of the eval usage here and would have liked to have a native implementation but it is not available.

Can we do any better? How do other frameworks like nodejs handle require? Does it use eval behind the scenes?