Say you have some code like this:

functiongetData (cb) {
  console.log("doing long async operation")
  http.get('/user', cb)
}

getData(function(err, data) {
  console.log("got 1")
})

getData(function(err, data) {
  console.log("got 2")
})

doing long async operation
doing long async operation
got 1
got 2

getData is a nice abstraction but every function that calls it will do an additional http request!

async.memoize

var getData = async.memoize(function(cb) {
  console.log("doing long async operation")
  http.get('/user', cb)
})

getData(function(err, data) {
  console.log("got 1")
})

getData(function(err, data) {
  console.log("got 2")
})

doing long async operation
got 1
got 2

async.memoize saves the day!