I (heart)Callbacks

callbacks1.js

function greet(user, cb) {
  users.findOne(user.name, function (err, result) {
    if (err) {
      cb(err);
    } else {
      var fullname = result.fullname;
      var email = result.email;
      var language = result.language;
      greetings.findOne(language, function (err, result) {
        if (err) {
          cb(err);
        } else {
          var body = result + fullname;
          nodemailer.send(email, body, function (err, result) {
            if (err) {
              cb(err);
            } else {
              cb(null, "Greeted " + fullname + " in " + language);
            }
          });
        }
      });
    }
  });
}

callbacks2.js

function greet(user, cb) {

  users.findOne(user.name, getGreeting);

  function getGreeting (err, result) {
    if (err) {
      cb(err);
    } else {
      var fullname = result.fullname;
      var email = result.email;
      var language = result.language;
      greetings.findOne(language, sendGreeting);
    }

    function sendGreeting (err, result) {
      if (err) {
        cb(err);
      } else {
        var body = result + fullname;
        nodemailer.send(email, body, showResult);
      }
    }
  
    function showResult(err, result) {
      if (err) {
        cb(err);
      } else {
        cb(null, "Greeted " + fullname + " in " + language);
      }
    }
  }  
}

callbacks3.js

function greet(user, cb) {
  
  // Putting shared variables in the outer scope
  var fullname = null;
  var email = null;
  var language = null;
  
  users.findOne(user.name, getGreeting);
 
  function getGreeting (err, result) {
    if (err) {
      cb(err);
    } else {
      fullname = result.fullname;
      email = result.email;
      language = result.language;
      greetings.findOne(language, sendGreeting);
    }
  }
 
  function sendGreeting (err, result) {
    if (err) {
      cb(err);
    } else {
      var body = result + fullname;
      nodemailer.send(email, body, showResult);
    }
  }
  
  function showResult(err, result) {
    if (err) {
      cb(err);
    } else {
      cb(null, "Greeted " + fullname + " in " + language);
    }
  }
  
}

callbacks4.js

function greet(user, cb) {
  
  var fullname = null;
  var email = null;
  var language = null;
  
  users.findOne(user.name, getGreeting);
 
  function getGreeting (err, result) {
    if (err) {
      return cb(err);
    }
    fullname = result.fullname;
    email = result.email;
    language = result.language;
    greetings.findOne(language, sendGreeting);
  }
 
  function sendGreeting (err, result) {
    if (err) {
      return cb(err);
    }
    var body = result + fullname;
    nodemailer.send(email, body, showResult);
  }
  
  function showResult(err, result) {
    if (err) {
      return cb(err);
    }
    cb(null, "Greeted " + fullname + " in " + language);
  }
  
}