How can I return javascript from a controller actionresult using ContentResult?

Question

I'm wondering how I can return a javascript alert when the file that usually gets generated is not created in the folder. When the else statement is ran, it returns the literal text at the top of the browser tab instead of the alert that I am looking for. It looks like this:

Code:

public ActionResult DownloadFile(string path, string fileName)
{
    if (System.IO.File.Exists(path))
    {
        byte[] fileBytes = System.IO.File.ReadAllBytes(path);
        return File(fileBytes, "application/force-download", fileName);
    }
    else 
    {
        return Content("<script language='javascript' type='text/javascript'>alert('No data was found to create a CSV file!');</script>");

    }
}

Content() sets the http content type header to "text/plain". That's why no html is rendered. See learn.microsoft.com/en-us/dotnet/api/… to return html with correct status code — Christoph Lütjen
– Christoph Lütjen, Commented Jun 8, 2020 at 18:50
@ChristophLütjen I've added a contentType parameter with "text/javascript", and that does not seem to change the output. — sjohn285
– sjohn285, Commented Jun 8, 2020 at 18:58
Given your example, you're returning html (text/html) not javascript. — Christoph Lütjen
– Christoph Lütjen, Commented Jun 9, 2020 at 9:13

Yiyi You · Accepted Answer · 2020-06-09 03:39:24Z

Firstly you can use the method public virtual ContentResult Content(string content, string contentType); rather than public virtual ContentResult Content(string content);

Controller:

public ActionResult DownloadFile()
        {
            return Content("alert('No data was found to create a CSV file!');", "application/javascript");
        }

In addition,you can also write a result which has a Parametrical constructor and extends ContentResult.You can refer to it

Here is a demo worked: Controller:

public ActionResult DownloadFile()
    {
        //return Content("alert('No data was found to create a CSV file!');", "application/javascript");
        return new JavaScriptResult("alert('No data was found to create a CSV file!');");
    }
    public ActionResult DownloadFile1() {
        return View();
    }

    public class JavaScriptResult : ContentResult
    {
        public JavaScriptResult(string script)
        {
            this.Content = script;
            this.ContentType = "application/javascript";
        }
    }

DownloadFile1:

@{
    ViewData["Title"] = "DownLoadFile1";
}

<h1>DownLoadFile1</h1>

<div>
    <partial name="DownLoadFile" />
</div>
@section scripts{
    <script src="~/lib/jquery/dist/jquery.min.js"></script>
    <script>
        $(function () {
            $.getScript("/Test/DownloadFile");
        });
    </script>
}

Result:

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