Offline syncing functionality via a service worker
Last updated a year ago by hash-bang .
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$ cnpm install @momsfriendlydevco/offline 
SYNC missed versions from official npm registry.

Offline ServiceWorker

Provide offline syncing functionality via a service worker.

This unit works by reading package declarations from the config, syncing those when internet is available and providing its own micro-ReST server when not.

It works by using the new Service Worker browser technology which sits between the requesting browser and the server which can mediate requests.


The syncing process is made up of the following steps. FE is the front end, BE the backend and SW the service worker

  1. [FE] Send a message to the Service Worker to sync
  2. [SW] Setup a cache
  3. [SW] Fetch resources from the server
  4. [BE] Compute a list of resources - this is the flattened version of app.config.offline.packages[] specific to the active user with all dependencies resolved
  5. [SW] Compose a list of all resources to check
  6. [SW] Request each resource as a list, if the resource is a collection try to optimize this by fetching the collection IDs + version only then compare, if the resource is a URL just pull it


As Service Workers are self contained JS files injecting the offline configuration is somewhat complex.

The easiest method is simply to use the supplied gulp build process while specifying a source file from where the config can be retrieved.

gulp build

In the above ./my-config.js is expected to export a JavaScript object which will be stringified and used as the offline config.

Config options:

Property Type Description
enabled boolean Whether the service worker is enabled
cleanInterval number Time in milliseconds between cleans
debug boolean Whether the service worker should output debugging messages
debugFailures boolean Whether all failures should be cached in caches/failures
debugPrefix string The prefix to use when debugging
fetchOptions object Additional options to pass into fetch()
fetchAttempts number The number of retry attempts before failing sync on network errors
fetchConcurrent number Number of concurrent requests allowed by Promise.allLimit()
forceOffline boolean If true, treat all incoming connections as offline (inherited from caches/meta/flags/forceOffline{enabled: true} if its present)
autoSyncFirst number Time in milliseconds until first sync (falsy to disable)
autoSyncPollingOnline number Time in milliseconds between polls after the first sync when we are online
autoSyncPollingOffline number Time in milliseconds between polls after the first sync when we are offline
ignore array <string> List of RegExps to skip caching for (these have to be strings to survive JSON encoding)
maxPostCycles number Maximum number of recursive post attempts before giving up, set this to the ideal depth of A creates B creates C style loops that are possible
packages array <object> Package specification, see below

The base config file is used to set the above to appropriate defaults. The object resolved by the file at OFFLINE_CONFIG_FILE override those defaults.

Config Package declaration

The offline.packages object is composed as a collection with the following properties:

Property Type Description
id string The unique ID to identify the package
title string The human friendly string to refer to the package
description string A longer description of the package
payload array A list of resources that should be pulled within this package

Payload us an array of the following objects:

Property Type Default Description
type string How the resource is mediated. Enum of: "url", "collection"
url string The URL to pull the resource from, use {{id}} as a specifier when iterating over a collection
version boolean Calculated Look for versioning information when pulling the resource, set to falsy to force 304 validation instead of using __v values. This is assumed true for type == 'collection' and false otherwise
create boolean false (If type==collection) specifies that posting to the URL will be handled as a document creation
count boolean true (If type==collection) specifies that the count of documents matching should be returned
query boolean true (If type==collection) specifies that ReST / Mongo / Sift style queries should provide a list of matching documents
post boolean false (If type==collection) specifies that posting to the URL will be handled as a document update

Current Tags

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2 Versions

  • 0.0.1                                ...           a year ago
  • 0.0.0                                ...           a year ago
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