1. functional js: extracting common protocols via https://youtu.be/kA4-b7hvWhg

after.js

// 1. extract what is common
function executeWithConnection(functionToExecute, argument) {
   try {
    var db = connectToDataBase(credentials());
    functionToExecute(db, asSqlInsert(track));
  }
  catch(e) {
    handleDatabaseError(e);
  }
}

// 2. refactor the orignal functions
function addUser(db, user) {
  execute(db, asSqlInsert(user));
}

function addTrack(db, track) {
  execute(db, asSqlInsert(track));
}

// 3. call with common function
executeWithConnection(addUser, {'name': 'Byron'});
executeWithConnection(addTrack, {'title': 'The JS Blues'});

before.js

// we see a lot of this
function addUser(user) {
  try {
    var db = connectToDataBase(credentials());
    execute(db, asSqlInsert(user));
  }
  catch(e) {
    handleDatabaseError(e);
  }
}

function addTrack(track) {
  try {
    var db = connectToDataBase(credentials());
    execute(db, asSqlInsert(track));
  }
  catch(e) {
    handleDatabaseError(e);
  }
}