UseNodeModules Updated for .NET Core 3

UseNodeModules is a NuGet package I put together a few years ago. The package gives you an easy way to install middleware for serving content directly from the node_modules folder in an ASP.NET Core project.

 public void Configure(IApplicationBuilder app)
{
    app.UseNodeModules(maxAge: TimeSpan.FromSeconds(600));
}

The idea is that during development you can use npm to manage all your client-side dependencies and you can use those dependencies immediately instead of setting up a process to copy files into the wwwroot folder. In production, you might use environment tag helpers to serve files you’ve bundled during a build, or to use minified files from a CDN. During development, however, you don’t have to wait for bundling, minification, and copying to occur.

Here's an example with Bootstrap 4. In development we'll serve directly from the node_modules folder. In any other environment we'll serve a minified file from a CDN, but with fallbacks to the node_modules folder in case the CDN is unavailable.

<environment include="Development">
    <link href="~/node_modules/bootstrap/dist/css/bootstrap.css" rel="stylesheet" />
</environment>
<environment exclude="Development">
    <link rel="stylesheet" href="//ajax.aspnetcdn.com/ajax/bootstrap/4.3.1/css/bootstrap.min.css"
    asp-fallback-href="~/lib/bootstrap/dist/css/bootstrap.min.css"
    asp-fallback-test-class="sr-only" asp-fallback-test-property="position" asp-fallback-test-value="absolute" />
</environment>

Be aware that dotnet publish will not copy the node_modules folder to the published output directory. You can change this behavior by adding the following to the .csproj file.

<ItemGroup>
    <Content Include="node_modules\**" CopyToPublishDirectory="PreserveNewest" />
</ItemGroup>

A nice side benefit of the above code is how Visual Studio users will also see node_modules in the Solution Explorer view. Otherwise, the folder is hidden by Visual Studio, which I’ve never understood.

Thanks to Shawn Wildermuth for the help!