Скачать или смотреть How to Successfully Return a Value from a JavaScript Input Prompt Box to C# in Blazor Server

Discover how to correctly return values from a JavaScript prompt box to C# within a Blazor Server application. Learn the common pitfalls and solutions with our clear guide.
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This video is based on the question https://stackoverflow.com/q/67928226/ asked by the user 'Baba' ( https://stackoverflow.com/u/2320476/ ) and on the answer https://stackoverflow.com/a/67928373/ provided by the user 'Nikki9696' ( https://stackoverflow.com/u/456669/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Challenge: Returning Values from JavaScript to C#

If you're developing a Blazor Server application, a common scenario arises when you want to gather user input through a JavaScript prompt and then use that input in your C# code. However, this process is not always seamless, especially when signals from JavaScript don’t translate properly into C# . Let’s explore a specific problem encountered by a developer trying to accomplish this task.

The Problem

A Blazor developer had the following button component in their application:

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

Upon clicking the button, a method GetUserInput is invoked that attempts to get a user’s name using a JavaScript prompt:

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

The corresponding JavaScript function looks like this:

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

However, this code crashes with the following error message:

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

This indicates that the JavaScript engine does not recognize retval, pointing towards a potential typo or case sensitivity issue.

The Solution: Fixing the JavaScript Reference

The crux of the problem lies in how JavaScript handles variable names. JavaScript is case sensitive, meaning retVal and retval are treated as entirely different variables. In this case, retval is not defined, which triggers the error.

Steps to Fix the Issue

Correct the Variable Name: Change the reference from retval to retVal in your return statement. Here’s the corrected code:

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

Why This Works

Case Sensitivity: As mentioned, JavaScript is case sensitive. By ensuring that the case of your variable names matches throughout your function, you're avoiding accidental errors that arise from typos.

Error Prevention: Avoiding undefined variables not only prevents crashes but also helps maintain clearer and more maintainable code.

Conclusion

By making a small change to your JavaScript function, you can effectively retrieve user input from a prompt and pass it back to your Blazor C# code. Always remember to double-check variable names for case sensitivity in JavaScript to avoid similar issues in the future. If you're facing input-related challenges in your Blazor applications, now you know how to troubleshoot effectively.

Happy coding!