What async level-hooks could look like

async-hooks.js

var LevelUp = require('levelup');
var Sublevel = require('level-sublevel')

var dbLoc = './test'
var opts = {valueEncoding: 'json'}
var db = Sublevel(LevelUp(dbLoc, opts));

var pageviews = db.sublevel('pageviews')
var sessions = db.sublevel('sessions')

var updateSession = function(current, prev, cb) {
  var revenueChange = current.revenue - prev.revenue
  sessions.get(current.sessionId, function(err, session) {
    session.revenue += revenueChange
    sessions.put(current.sessionId, session, cb)
  })
}

pageviews.pre(function(change, add) {
  var current = change.value

  pageviews.get(change.key, function(err, prev) {
    if equals(current, prev) {
      add(false)
    } else {
      updateSession(current, prev)
      add(true) // ?
    }
  })
  
})

@dominictarr: re: async hooks in ##leveldb