Скачать или смотреть Solving the Blazor .Net App JavaScript Loading Issue in Docker Containers

Learn how to troubleshoot and solve the common issue of missing JavaScript and CSS files in your Blazor .NET app when deploying in Docker containers.
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Troubleshooting Missing JavaScript in Blazor .NET App in Docker Container

Deploying a Blazor .NET application into a Docker container may seem straightforward, but developers often face unexpected issues, particularly with missing files. In this guide, we will explore a specific problem: JavaScript and CSS files not loading correctly when deploying a Blazor app into a Linux Docker container.

Understanding the Problem

After setting up a Blazor app with Docker support, developers often add public NuGet packages to enhance functionality. However, despite successfully deploying DLLs, JavaScript files may not appear in the expected directories. The specific case we address here arose with the BlazorInputMask package, leading to 404 errors in the browser for certain JS files. This can be frustrating, especially as local debug runs may not exhibit the same behavior.

Steps to Reproduce the Issue

Here is a breakdown of how this issue may be encountered:

Start a new Blazor app with Docker support.

Add a public NuGet package, like BlazorInputMask.

Include the necessary references to the JavaScript files in the _Layout.cshtml:

[[See Video to Reveal this Text or Code Snippet]]

Run the app locally using the Docker debugger.

Check network calls in the browser, discovering a 404 - Main.js not found error.

Inspect the Docker container's file structure to confirm the absence of Main.js in the wwwroot directory.

Despite successful builds outside of containers, this problem persists uniquely within a Dockerized environment.

Finding the Solution

The resolution to this problem turned out to be relatively straightforward once the case of the filenames was examined.

Issue Identification

Upon closer examination, the documentation for the BlazorInputMask package referred to the JavaScript file as Main.js. However, in the package itself, the actual filename was main.js, indicating a case sensitivity problem inherent in Linux filesystem architecture. In Windows, filenames are not case-sensitive, meaning this error could easily go unnoticed.

Implementing the Fix

To rectify the situation, simply update the script references in your _Layout.cshtml file to match the actual filename as shown below:

[[See Video to Reveal this Text or Code Snippet]]

By ensuring that the case in your script references matches exactly with the file names used in the NuGet package, the application can successfully locate and load the required JavaScript files without triggering 404 errors.

Conclusion

Most deployment challenges can be frustrating, especially when the root cause stems from something as seemingly trivial as case sensitivity. If you encounter similar issues with missing JavaScript or CSS files in your Blazor .NET application while working in Docker containers, always check for case mismatches in your file names.

This case serves as a crucial reminder: when deploying applications to different environments, always be mindful of system peculiarities such as file system sensitivity.

By sharing this information, we hope to save fellow developers time and confusion in future deployments!