Self-updating Node.js module in ~39SLOC

tiny.js

var fs = require('fs')
var path = require('path')
var vm = require('vm')

module.exports = {
  
  watch:
    function (module) {
      fs.watch(module.filename, function (event, filename) {
        module.exports.changed(module, this, event, filename); }) },
  
  changed:
    function (module, watcher, event, filename) {

      if (event === 'rename' && !fs.existsSync(__filename)) {
        watcher.deleted = true;
        return console.log("<>", "delete", filename); }
      if (watcher.deleted) {
        event = 'create';
        delete watcher.deleted }
      console.log("<>", event, filename);
      
      var source = fs.readFileSync(__filename, 'utf8');
      /* at this point you can transform the source using babel, etc */
      if (module.source === source) return console.log('no changes');
      module.source = source;
      
      var context = module.exports.update(vm.createContext(global),
        { require:    require
        , module:     module
        , console:    console
        , process:    process
        , global:     global
        , __filename: __filename
        , __dirname:  __dirname });
      var options = { filename: __filename, displayErrors: true };
      vm.runInContext(source, context, options);
      
      console.log(module.exports);
      watcher.close(); },
  
  update:
    function (into, from) {
      for (key in from) into[key] = from[key];
      for (key in into) if (Object.keys(from).indexOf(key) < 0) delete into[key];
      return into; } }

module.exports.watch(module);