Blazor PWA


With the Web Assembly 3.2.0 Preview 3 release of the Blazor Web Assembly template you can now make a Progressive Web Application (PWA).  This can only be done with the web assembly because of the requirements for a PWA.

Before we can talk about the Blazor PWA, we need to make sure we understand what a PWA is.



Via Wikipedia:

“A progressive web application is a type of application software delivered through the web, built using common web technologies including HTML, CSS and JavaScript. It is intended to work on any platform that uses a standards-compliant browser.”


The key takeaway from the definition is the “works on any platform”.  Don’t just mobile, but Windows, Mac and even Chrome Book.

PWAs is not a new technology, it is just HTML, JS and CSS.  It is the packaging of these that make it a PWA.

Why build a PWA

Like most decision in development, the answer depends.  Sometimes this answer can be decided for non-technical reasons, Marketing, Branding etc.  But from the development side of the decision, there are a lot of factors that go into the choice:

      1.       You need a way to quickly get an application to user and can’t wait to go through the app stores
      2.       You have multiple platforms to support and your skill set is not in the native platforms
      3.       You don’t want to give Apple 30% of your revenue
      4.       You don’t need low level hardware access

Key Components

There are 3 core components that qualify an application to be considered a PWA:

   1.  Secure Communication
       a. Must communication via HTTPS
   2. Service Worker
       a. A javascirpt script that allows intercepting and control of how a web browser handles its network requests and asset caching.
       b. Creates reliably fast web pages
       c. Provides offline experiences.
   3. Manifest file
       a. Json formatted Meta Data about your application
       b. Controls how your app appears to the user

That is all that it takes to make any web application a PWA.
There are a ton of resources to help create the service worker and the manifest file.  See the end of the post for a list of those resources.

Blazor PWA Template


When you select the PWA check box on the create project selection, it will create the normal Web Assembly project but with the manifest file and the service worker script and will add those to the application.





Manifest File

Here is what is in the manifest file:

    {
      "name": "MyNewProject",
      "short_name": "MyNewProject",
      "start_url": "./",
      "display": "standalone",
      "background_color": "#ffffff",
      "theme_color": "#03173d",
      "icons": [
        {
          "src": "icon-512.png",
          "type": "image/png",
          "sizes": "512x512"
        }
      ]
   }

You do have to have icons listed for each platform for best results.

As you can see, it will only provide the bare minimum of the meta data you can have.  Listed in the resource below, there is a web site that will help you create the manifest file and help you create the FAVIcons for each platform.

Special note for Apple.  They have their own set of meta tags to use in order for the values to be seen properly on iOS.


Service Worker


The service worker is executed in a separate thread and is responsible for acting as a proxy for the web server.   It will intercept web request and allow you to do anything you need to do.  Such as pull from cache first, or from the server and even reroute if needed.

Here is the service worker script that the Blazor template uses:

        self.addEventListener('fetch', () => { });


That’s it.   Not much to it.  You can add all the functionality you may need to handle your application’s need.

As you can see there is not much to making any web application into a PWA.  When you use a PWA and when to go native is always a hard question.  There are times you have go native, but with the additional advantages that the PWA can give you, it is a now a little harder decision.  But with the PWA you at least now have a new tool to put in your toolbox.   

Additional Resources


        1.       You might not need electron 
        2.       Fav Icon Generator 
        3.       Intro to PWA 
        4.       What can the web do today 
        5.       PWA Builder 
        6.       LightHouse 
        7.       PWA Rocks 
        8.       Microsoft Dev Tools 
        9.       Iconic Blog 
        10.   Love2Dev

Simple HTML PWA Project 

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