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Explain the concept of cache manifest and its role in offline web applications.

Revati S Misra14324-May-2023

Explain the concept of cache manifest and its role in offline web applications.

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Updated on 25-May-2023
Revati S Misra

Revati S Misra

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Aryan Kumar

Aryan Kumar

25-May-2023

A cache manifest, also known as an "application cache", is a web browser mechanism that enables offline web application functionality. This allows developers to specify a list of resources that will be cached by the browser so they are available even if the device is offline. A cache manifest file is a plain text file with a specific format and .appcache extension.

Here's how the cache manifest works and its role in offline web applications:

  1. Cache manifest definition:
    A cache manifest file contains a list of resources such as HTML files, CSS style sheets, JavaScript files, images, and other assets to cache in the browser. Specifies resources that the browser should store locally for offline access. 
  2. Manifest File Declaration: To enable offline functionality, the web application's HTML file must include a reference to the cache manifest file using the manifest attribute in the html tag. For example:
<html manifest="myapp.appcache">
  1. Manifest File Structure: The cache manifest file consists of sections that define the behavior of the application cache. The main sections are:
  • CACHE: Lists the resources that should be cached and made available offline. Each resource is specified on a separate line.
  • NETWORK: Specifies resources that should be requested from the network and not cached.
  • FALLBACK: Defines fallback pages that should be displayed when a resource is inaccessible offline.
  1. Initial cache:
    When a user visits her web application for the first time, the browser downloads and saves all the resources specified in the cache manifest. These resources will be available for offline viewing.
  2. Subsequent cache:
    On subsequent visits, the browser compares the contents of the cached manifest file with the cached resources. If resources change or new resources are added, the browser updates its cache accordingly. This keeps the application cache up-to-date with the latest versions of resources. 
  3. Offline access:
    When the device is offline or no network connection is available, the web application uses cached resources from the application cache to render content. Users can interact with applications, access previously visited pages, and perform certain functions without an Internet connection.
  4. Update cache:
    To update the cache and ensure that your users get the latest content when online, you need to modify your cache manifest file. Developers can change the contents of the manifest file. For example, update the version number or change the list of resources. When the manifest file is updated, the browser detects the change and downloads new or changed resources and updates the application cache. 

Cache manifests play an important role in offline web applications because they allow developers to define and manage resources that are available for offline access. This provides a way to control caching behavior, allowing users to continue using applications without an internet connection, and automatically refreshing cached content when the device reconnects to the network. will be 

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