BufferQueue

The point of this JS library is to prioritise the download of a large number of binary files. It leverages the logic of a priority queue with multiple levels of priority. If N is the number of priority level you want, then 0 will be the highest priority and n-1 will be the lowest.

Each level is a first in first out list and each element is identified by its URL.

Install

npm install --save @jonathanlurie/bufferqueue

Usage

Instanciate the main object:

let myBufferQ = new bufferqueue.BufferQueue({
  priorityLevels: 5, // the number of priority level, N (default: 4)
  concurentDownloads: 4, // the number of concurrent downloads you allow. (Chrome allows a max of 6) (default: 3)
  httpSettings: {} // object containing the http header and other stuff (default: {})
})

To know more about the 'httpSettings' object, refer to the init object from Request documentation.

Since downloading file is an asynchronous process in Javascript, BufferQueue relies on custom events of different kinds:

• added: when a file is just being added to the queue

myBufferQ.on('added', function(url, priority){
  // do something with it
})

• removed: when a file is just being removed to the queue, without having started to get downloaded

myBufferQ.on('removed', function(url){
  // do something with it
})

• reseted: When the whole priority queue has be reseted

myBufferQ.on('reseted', function(){
  // do something with it
})

• downloading: when the download of a file is starting

myBufferQ.on('downloading', function(url){
  // do something with it
})

• failed: when the download of a file has failed

myBufferQ.on('failed', function(url, error){
  // do something with it
})

• aborted: when the download of a file has been explicitly aborted by the user

myBufferQ.on('aborted', function(url){
  // do something with it
})

• success: when is a file download is completed successfully. buffer is an ArrayBuffer and time is the download time is in millisecond (you can then compute the actual download rate)

myBufferQ.on('success', function(url, buffer, time){
  // do something with it
})

In addition to events, an instance of BufferQueue has some methods:

myBufferQ.add(
  'http://example.com/some-file', // URL
  0 // level of priority
)

The other other methods can be found in the documentation.