Async compatible Batch and Retry api requirements.

batcher.js

var batcher = require("batcher")

var myUploader = function(item, done){
  uploadSomewhere(item, function(err, result){
    done(err, result)
  })
}

var myErrCheck = function(err, retry, pass){
  if(err.statusCode == 503){
    retry()
  }else{
    pass()
  }
}

batcher.batch(["item1", "item2", "item3"], myUploader, { batchSize: 4, errFn: myErrCheck }, function(err, results){
  if(err){
    // we failed even after retrys
  }else{
    // all tasks are successful
  }
})

Third argument should be optional in which case it would default to batch size of 4 and perform no retries.

Third argument could also be a function in which case the batch size would default to 4.

Third argument could also be an integer in which case the batch size would change to value passed in and no retries would be performed.

It appears that async's eachLimit() is half of what we want. Just need to build an array of items to retry.

https://github.com/caolan/async#eachlimitarr-limit-iterator-callback