Introduction to Offline Progressive Web Applications

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Information about Introduction to Offline Progressive Web Applications

Published on September 16, 2017

Author: IliaIdakiev



2. WHY PWA? FAST - Respond quickly to user interactions with silky smooth animations and no janky scrolling. RELIABLE - Load instantly and never show the downasaur, even in uncertain network conditions. ENGAGING - Feel like a natural app on the device, with an immersive user experience.

3. OFFLINE PROGRESSIVE WEB APPLICATIONS SERVICE WORKERS ▸ Runs separately from the main browser thread ▸ Designed to be fully asynchronous ▸ Programmable network proxy ▸ Runs only over HTTPS ▸ Becomes idle when not in use and restarts when it's next needed.

4. OFFLINE PROGRESSIVE WEB APPLICATIONS ADVANCED FEATURES ▸ Notifications API - Display and interact with notifications using the operating system's native notification system. ▸ Push API: Subscribe to a push service and receive push messages. Push messages are delivered to a service worker, which can use the information in the message to update the local state or display a notification to the user. Because service workers run independently of the main app, they can receive and display notifications even when the browser is not running.

5. OFFLINE PROGRESSIVE WEB APPLICATIONS ADVANCED FEATURES ▸ Background Sync API: Defer actions until the user has stable connectivity. This is useful to ensure that whatever the user wants to send is actually sent. This API also allows servers to push periodic updates to the app so the app can update when it's next online. ▸ Channel Messaging API: Lets web workers and service workers communicate with each other and with the host application.


7. OFFLINE PROGRESSIVE WEB APPLICATIONS 1. REGISTRATION ▸ The scope of the service worker determines which files the service worker controls. The default scope is the location of the service worker file, and extends to all directories below. An arbitrary scope can also be set by passing in an additional parameter when registering.

8. OFFLINE PROGRESSIVE WEB APPLICATIONS 2. INSTALLATION ▸ This occurs if the service worker is considered to be new by the browser. ▸ During the install, service workers can precache parts of a web app so that it loads instantly the next time a user opens it.

9. OFFLINE PROGRESSIVE WEB APPLICATIONS 3. ACTIVATION ▸ If there are any open pages controlled by the previous service worker, the new service worker enters a waiting state. ▸ The new service worker only activates when there are no longer any pages loaded that are still using the old service worker. This ensures that only one version of the service worker is running at any given time. ▸ When the new service worker activates, an activate event is triggered in the activating service worker. This event listener is a good place to clean up outdated caches.

10. OFFLINE PROGRESSIVE WEB APPLICATIONS OTHER EVENTS ▸ message - service worker can receive information from other scripts ▸ fetch - intercept requests. ▸ push - when a (Web Push Protocol) message is received. ▸ sync - ask for an event to be fired when the user has connectivity and we listen for it


12. OFFLINE PROGRESSIVE WEB APPLICATIONS CACHE API ▸ Lets us create stores of responses keyed by request. ▸ Exposed on the window so it accessed from anywhere in your scripts via "caches". ▸ waitUntil extends the lifetime of the install event until the passed promise resolves successfully. If the promise rejects, the installation is considered a failure and this service worker is abandoned (if an older version is running, it stays active).

13. OFFLINE PROGRESSIVE WEB APPLICATIONS CACHE FALLING BACK TO THE NETWORK ▸ To serve content from the cache and make your app available offline you need to intercept network requests and respond with files stored in the cache.

14. OFFLINE PROGRESSIVE WEB APPLICATIONS ALL APPROACHES ▸ cache only ▸ network only ▸ cache falling back to network ▸ network falling back to cache ▸ cache then network



17. OFFLINE PROGRESSIVE WEB APPLICATIONS APPLICATION MANIFEST JSON ▸ Web app manifests provide the ability to save a site bookmark to a device's home screen. When a site is launched this way: ▸ It has a unique icon and name so that users can distinguish it from other sites. ▸ It displays something to the user while resources are downloaded or restored from cache. ▸ It provides default display characterstics to the browser to avoid too abrupt transition when site resources become available.



20. OFFLINE PROGRESSIVE WEB APPLICATIONS HYPERTEXT TRANSFER PROTOCOL VERSION 2 (HTTP/2) ▸ Data compression of HTTP headers (HPACK) ▸ encode large headers using a fixed Huffman encoding ▸ encode commonly used headers as a variable length integer, rather than re-sending the whole header each time ▸ HTTP/2 Server Push ▸ Multiplexing multiple requests over a single TCP connection ▸ Every request/response pair is mapped to a stream. Each stream is given a unique id. ▸ Priority - Allow a client to give priority preferences to particular streams ▸ Flow Control - Every stream, and the connection as a whole maintains a send window, which is the amount of data that the server is allowed to send on the stream/connection.

21. OFFLINE PROGRESSIVE WEB APPLICATIONS SERVER SIDE RENDERING ▸ First Meaningful Paint - The time at which the user feels that the primary content of the page is visible. ▸ Rendering front-end JavaScript applications on the server.



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