# Async
- http://caolan.github.io/async/

## waterfall
```js
async.waterfall([
  function(callback) {
    callback(null, 'one', 'two');
  },
  function(arg1, arg2, callback) {
    // arg1 now equals 'one' and arg2 now equals 'two'
    callback(null, 'three');
  },
  function(arg1, callback) {
    // arg1 now equals 'three'
    callback(null, 'done');
  }
], function (err, result) {
  // result now equals 'done'
});

// Or, with named functions:
async.waterfall([
  myFirstFunction,
  mySecondFunction,
  myLastFunction,
], function (err, result) {
  // result now equals 'done'
});
function myFirstFunction(callback) {
  callback(null, 'one', 'two');
}
function mySecondFunction(arg1, arg2, callback) {
  // arg1 now equals 'one' and arg2 now equals 'two'
  callback(null, 'three');
}
function myLastFunction(arg1, callback) {
  // arg1 now equals 'three'
  callback(null, 'done');
}
```