Configuring Lazy Loading @ WebAssembly

The following nuget package includes everything you need to support lazy loading on Blazor WebAssembly (when statically published, using DevServer or using DualMode).

It can be installed by adding the following line inside the host csproj:

<PackageReference Include="BlazorLazyLoading.Wasm" Version="1.3.0" PrivateAssets="all" />

It will also require to be initialized from Program.cs by adding the following lines:

builder.Services.AddLazyLoading(new LazyLoadingOptions
{
    ModuleHints = new[] { "ModulesHost" }
});

Configuring the Linker

In order to load assemblies dynamically, the linker can be a big issue since it is enabled for release builds by default.

There are 2 ways of approaching this:

Disabling the Linker (easy)

This option sounds worse that it is in reality. Yes, disabling the linker will ship mscorlib as initial download to the browser, BUT that's all. The initial impact won't be big if we Lazy Load the rest of the application.

<PropertyGroup>
    <BlazorWebAssemblyEnableLinking>false</BlazorWebAssemblyEnableLinking>
</PropertyGroup>

Using LinkerConfig.xml (advanced)

Even if this solution is more advanced, it will give us the best performance. Please refer to the following guide to setup your LinkerConfig.xml.

The recommendation here would be something like this, but you might need to adapt it for your needs:

<?xml version="1.0" encoding="UTF-8" ?>
<linker>
    <assembly fullname="netstandard" /> <!-- keep full netstandard since its used by the lazy modules -->
    <assembly fullname="ModulesHost" /> <!-- keep full entrypoint -->
</linker>

Done! Lazy Loading is now configured 😄

Due to a bug in Blazor's linker, the user assemblies will be downloaded as part of the boot but not in memory. The library handles this case gracefully so it shouldn't be a problem until the linker gets fixed. More info...

LazyLoadingOptions

• ModuleHints

  In order to find the _lazy.json manifest files and DLLs, you need to specify at least an entry-point to a lazy module. This must be done by passing the "known modules" as string.

  Specifies a list of Module Names (hints) to:

  • Download DLLs from them
  • Use their manifest to locate lazy resources