javascript – file is being assigned a //# sourceMappingURL but already has one-ThrowExceptions

Exception or error:

I just notice Firefox console outputs the following error for every single .js/.coffee file in my project (even the packages).

-file- is being assigned a //# sourceMappingURL, but already has one

Chrome’s console doesn’t show anything. I tried deleting all the .map files and clearing Firefox’s cache but I’m still getting the errors.

How to solve:

It’s a warning (not an error)
and it is a bug ( fixed in FF 33)

This warning/error also applies to other libs (angular, backbone, etc.)


I have been working on a project for over a year now, I have never seen this message until roughly the last Firefox update.

I received it using jQuery 1.9.x, so I just updated my jQuery to 1.11.x and the error went away. I am now happy.

So, if you are using jQuery and see this Error/Warning, try updating your jQuery to the latest version.

Hope this helps someone.


In Firefox 27.0.1 I was getting this exact same error. I already have jQuery 1.11.0.

SyntaxError: Using //@ to indicate sourceMappingURL pragmas is deprecated.
Use //# instead kendo.dataviz.min.js:25
22:09:26.635 Error: http://localhost/project/Scripts/kendo.dataviz.min.js is being assigned a //# sourceMappingURL, but already has one

I opened the kendo.dataviz.min.js and deleted the offending line:



put your code inside

   $( document ).ready(function() {

then the message dissappears.


For the people using Visual Studio 2013, and have downloaded the jQuery libraries via NuGet, check your jquery-x.x.x.min.js and you’ll find the text comment below that’s popping this warning on Firefox.

// #

You can safely remove those lines.


Update jquery – from the jQuery website

You can also download a sourcemap file for use when debugging with a compressed file. The map file is not required for users to run jQuery, it just improves the developer’s debugger experience. As of jQuery 1.11.0/2.1.0 the //# sourceMappingURL comment is not included in the compressed file.

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