Why does ASP.NET Core 9 strip out importmap?

I have seen this on a newly-generated ASP.NET Core 9 app and in an app I upgraded to .NET 9 from .NET 8.

This is in Views/Shared/_Layout.cshtml:

   <script type="importmap">
      {
        "imports": {
            "axios": "/js/axios.min.js",
            "axios-retry": "/js/axios-retry.js",
            "is-retry-allowed": "/js/is-retry-allowed.js"
        }
      }
   </script>

and it gets stripped out. When I look at the devtools/sources tab in Chrome, it's there for the .NET 8 app, but not for the .NET 9 app.

How do I stop .NET 9 from doing that?

Edit: I found that the ScriptTagHelper class is the culprit.

If I add the following to _ViewImports.cshtml the importmap is not stripped out:

@removeTagHelper Microsoft.AspNetCore.Mvc.TagHelpers.ScriptTagHelper, Microsoft.AspNetCore.Mvc.TagHelpers

I'm guessing I don't want the ScriptTagHelper class permanently disabled (or do I?). Is there a way to tell it "leave my importmap alone"?

Solution

After checking the source code, you are missing asp-importmap when using importmap.

Source code links:

private const string ImportMapAttributeName = "asp-importmap";

If we are missing asp-importmap attribute, we will get null exception in below code. That's why the script content not render in broswer.

var importMap = ImportMap ?? ViewContext.HttpContext.GetEndpoint()?.Metadata.GetMetadata();

Here is the soultion

@using Microsoft.AspNetCore.Components
@{
    var data = new ImportMapDefinition(
        new Dictionary<string, string>
        {
            { "axios", "/js/axios.min.js" },
            { "axios-retry", "/js/axios-retry.js" },
            { "is-retry-allowed", "/js/is-retry-allowed.js" },
        },null,null);
}
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>@ViewData["Title"] - _79279047_1</title>
    <script type="importmap" asp-importmap="@data"></script>

    <link rel="stylesheet" href="~/lib/bootstrap/dist/css/bootstrap.min.css" />
    <link rel="stylesheet" href="~/css/site.css" asp-append-version="true" />
    <link rel="stylesheet" href="~/_79279047_1.styles.css" asp-append-version="true" />
</head>
<body>
    <header>
        <nav class="navbar navbar-expand-sm navbar-toggleable-sm navbar-light bg-white border-bottom box-shadow mb-3">
            <div class="container-fluid">
                <a class="navbar-brand" asp-area="" asp-controller="Home" asp-action="Index">_79279047_1</a>
                <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target=".navbar-collapse" aria-controls="navbarSupportedContent"
                        aria-expanded="false" aria-label="Toggle navigation">
                    <span class="navbar-toggler-icon"></span>
                </button>
                <div class="navbar-collapse collapse d-sm-inline-flex justify-content-between">
                    <ul class="navbar-nav flex-grow-1">
                        <li class="nav-item">
                            <a class="nav-link text-dark" asp-area="" asp-controller="Home" asp-action="Index">Home</a>
                        </li>
                        <li class="nav-item">
                            <a class="nav-link text-dark" asp-area="" asp-controller="Home" asp-action="Privacy">Privacy</a>
                        </li>
                    </ul>
                </div>
            </div>
        </nav>
    </header>
    <div class="container">
        <main role="main" class="pb-3">
            @RenderBody()
        </main>
    </div>

    <footer class="border-top footer text-muted">
        <div class="container">
            &copy; 2024 - _79279047_1 - <a asp-area="" asp-controller="Home" asp-action="Privacy">Privacy</a>
        </div>
    </footer>
    <script src="~/lib/jquery/dist/jquery.min.js"></script>
    <script src="~/lib/bootstrap/dist/js/bootstrap.bundle.min.js"></script>
    <script src="~/js/site.js" asp-append-version="true"></script>
   

    @await RenderSectionAsync("Scripts", required: false)
</body>
</html>

Test Result