module.exports와 exports

# write file with printf
$ printf "// module.exports\nmodule.exports.add = function (a, b) { return a + b; };\n\n// exports\nexports.add = function (a, b) { return a + b; };\n\n// this\nthis.add = function (a, b) { return a + b; };" > math.js

# execute node.js
$ node

> const math = require('./math');
undefined
> math
{ add: [Function] }
> math.add(42, 5);
47