Recursive require crashes node

foo.js

module.exports = foo;

require('./index.js')();

function foo(){
  console.log('foo.js', Date.now() );
}

index.js

module.exports = index;

require('./foo.js')();

function index(){
  console.log('index.js', Date.now());
}

How can I do this:

module.exports = index;

require('./foo.js')();

var index = function(){
  console.log('index.js', Date.now());
}