Chrome refuses to execute an AJAX script due to wrong MIME type

Question

By adding a callback argument, you are telling jQuery that you want to make a request for JSONP using a script element instead of a request for JSON using XMLHttpRequest.

JSONP is not JSON. It is a JavaScript program.

Change your server so it outputs the right MIME type for JSONP which is application/javascript.

(While you are at it, stop telling jQuery that you are expecting JSON as that is contradictory: dataType: 'jsonp').

If your proxy server or container adds the following header when serving the .js file, it will force some browsers such as Chrome to perform strict checking of MIME types:

X-Content-Type-Options: nosniff

Remove this header to prevent Chrome performing the MIME check.

FYI, I've got the same error from Chrome console. I thought my AJAX function causing it, but I uncommented my minified script from /javascripts/ajax-vanilla.min.js to /javascripts/ajax-vanilla.js. But in reality the source file was at /javascripts/src/ajax-vanilla.js. So in Chrome you getting bad MIME type error even if the file cannot be found. In this case, the error message is described as text/plain bad MIME type.

For the record and Google search users, If you are a .NET Core developer, you should set the content-types manually, because their default value is null or empty:

var provider = new FileExtensionContentTypeProvider();
app.UseStaticFiles(new StaticFileOptions
{
    ContentTypeProvider = provider
});