checkpoint-stream

> Queue data from a stream until a checkpoint is hit

``sh
$ npm install --save checkpoint-stream
`
`js
var checkpoint = require('checkpoint-stream')

// getObjectsStream() returns a stream that emits multiple objects
// this will queue up those objects until we reach a checkpoint
// once the isCheckpointFn test passes, the queue is flushed

getObjectsStream()
.on('error', function() {...})
.pipe(checkpoint.obj(function(obj) {
return typeof obj.token !== 'undefined'
}))
.on('checkpoint', function(obj) {
// the obj from getObjectsStream() that passed the isCheckpointFn test
})
.on('data', function(obj) {
// emitted for each object
})
`

$3

Say you're working with a streaming API that returns many results. Anywhere during transmission, the API call could fail. The API knows this, so it periodically returns a token you can use when you retry the request.

When you get a result that has that token, that's kind of like a "checkpoint". It means, release all the results we've received up until now, because we know we'll be able to pick up from here when we go to retry the request.

API

$3

- Returns TransformStream (via through2)

$3

- Returns TransformStream (via through2)

#### config

- Required
- Type: Object or Function

A configuration object. If a function is provided, it is treated as config.isCheckpointFn.

##### config.isCheckpointFn

- Required
- Type: Function

This function will receive each data event that is emitted from the source stream. Return a boolean to indicate if this is a checkpoint or not. If it is a checkpoint, this event, and any previously queued events before it will be passed through to the next stream in your pipeline. If it is not a checkpoint, this event will be queued until you return true in a future data event.

##### config.maxQueued

- Optional
- Type: Number
- Default: 10

Configure how many results will be queued before they are released, regardless of if a checkpoint has been reached.

##### config.objectMode

- Optional
- Type: Boolean
- Default: false

Enable objectMode` when dealing with streams in object mode.