If a forked node process exits, how can the parent know?

child.js

console.log('child spawned');

process.on('exit', function() {
  // This never executes.
  process.send('exited from within child');
});

function tellParentImDone() {
  process.send('hey parent, all done');
}

// WHOOPS BROKEN 3RD PARTY CODE FORGOT TO DO THIS
// tellParentImDone();

parent.js

// Run with: node parent.js

var fork = require('child_process').fork;
var child = fork('child.js');

child.on('exit', allDone.bind(null, 'exit'));
child.on('message', allDone.bind(null, 'message'));

function allDone(mode, arg) {
  console.log(mode + ':', arg);
  child.kill();
}