Playing with promises

promise_play.js

var p = require("p-promise");

var promise = p.defer();

promise.then(function() {
    fs.readFile("sample.json", 'utf8');
  })
  .then(function(data) {
    var o = JSON.parse(data);
    o.foo = "bar";
    fs.writeFile("sample.json", JSON.stringify(o), {encoding: 'utf8'});
  })
  .then(function() {
    console.log("Finished");
  });