Blazor Web Assembly large app size

There is a gotcha when crating Blazor application from the template that includes service worker (PWA support enabled). Notice that the service worker is pre-fetching all the static assets (files like JavaScript, CSS, images). See this code on GitHub as an example of the code generated by the default dotnet template for web assembly with PWA.

If you are using a bootstrap like then web assets folder will include all the plugins that the bootstrap comes with. You may use just 1% of the bootstrap functionality, but default service worker will pre-fetch all unused assets.

That can easily make initial size of the app loaded in the browser be around 40 MB (in the release mode). Do not think that all that files are necessary .net framework libraries loaded as web assembly. When looking into the network tab you’ll notice that most of the resources are js/css files that you had probably never used in your app.

Normal web assembly application size created with Blazor, even on top of the bootstrap or components library like (or both), should be less than 2 MB of network resources (excluding images that you may have).

So, please watch out for the default PWA service worker. It can make initial app loading time unnecessary long. If you are not providing any offline functionality, the easiest solution is just to remove service worker from your project by removing it from index.html file. Another option is to craft includes path pattern to include only what is really used.

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