Perhaps I'm missing something, but the docs seem to be incorrect in stating how to 'require' this lib, i.e.
'use strict';
var j2c_test1 = require('j2c');
console.log(j2c_test1.sheet); // undefined
var j2c_test2 = require('j2c')();
console.log(j2c_test2.sheet); // [function body]
Note the function call for j2c_test2
I'm using Browserify with Babelify, if that makes any difference :)