jQuery's jquery-1.10.2.min.map is triggering a 404 (Not Found)

I'm seeing error messages about a file, min.map, being not found:

GET jQuery's jquery-1.10.2.min.map is triggering a 404 (Not Found)

Screenshot

Where is this coming from?

If Chrome DevTools is reporting a 404 for a .map file (maybe jquery-1.10.2.min.map, jquery.min.map or jquery-2.0.3.min.map, but can happen with anything) first thing to know is this is only requested when using the DevTools. Your users will not be hitting this 404.

Now you can fix this or disable the sourcemap functionality.

Fix: get the files

Next, it's an easy fix. Head to http://jquery.com/download/ and click the Download the map file link for your version, and you'll want the uncompressed file downloaded as well.

Having the map file in place allows you do debug your minified jQuery via the original sources, which will save a lot of time and frustration if you don't like dealing with variable names like a and c.

More about sourcemaps here: An Introduction to JavaScript Source Maps

Dodge: disable sourcemaps

Instead of getting the files, you can alternatively disable JavaScript source maps completely for now, in your settings. This is a fine choice if you never plan on debugging JavaScript on this page. Use the cog icon in the bottom right of the DevTools, to open settings, then:

You can remove the 404 by removing the line

//@ sourceMappingURL=jquery-1.10.2.min.map

from the top part of your jQuery file.

The top part of the jQuery file will look like this.

/*! jQuery v1.10.2 | (c) 2005, 2013 jQuery Foundation, Inc. | jquery.org/license
//@ sourceMappingURL=jquery-1.10.2.min.map
*/

Just change that to

/*! jQuery v1.10.2 | (c) 2005, 2013 jQuery Foundation, Inc. | jquery.org/license */

Purpose of a source map

Basically it's a way to map a combined/minified file back to an unbuilt state. When you build for production, along with minifying and combining your JavaScript files, you generate a source map which holds information about your original files. When you query a certain line and column number in your generated JavaScript you can do a lookup in the source map which returns the original location. Developer tools (currently WebKit nightly builds, Google Chrome, or Firefox 23+) can parse the source map automatically and make it appear as though you're running unminified and uncombined files. (Read more on this here)

As it is announced in jQuery 1.11.0/2.1.0 Beta 2 Released the source map comment will be removed so the issue will not appear in newer versions of jQuery.

Here is the official announcement:

One of the changes we’ve made in this beta is to remove the sourcemap comment. Sourcemaps have proven to be a very problematic and puzzling thing to developers, generating scores of confused questions on forums like StackOverflow and causing users to think jQuery itself was broken.

Anyway, if you need to use a source map, it still be available:

We’ll still be generating and distributing sourcemaps, but you will need to add the appropriate sourcemap comment at the end of the minified file if the browser does not support manually associating map files (currently, none do). If you generate your own jQuery file using the custom build process, the sourcemap comment will be present in the minified file and the map is generated; you can either leave it in and use sourcemaps or edit it out and ignore the map file entirely.

Here you can find more details about the changes.

Here you can find confirmation that with the jQuery 1.11.0/2.1.0 Released the source-map comment in the minified file is removed.

1. Download the map file and the uncompressed version of jQuery.
   Put them with the minified version:

   

2. Include minified version into your HTML:

   

3. Check in Google Chrome:

   

4. Read Introduction to JavaScript Source Maps

5. Get familiar with Debugging JavaScript

The new versions of jQuery require this file http://code.jquery.com/jquery-1.10.2.min.map

The usability of this file is described here http://www.html5rocks.com/en/tutorials/developertools/sourcemaps/

Update:

jQuery 1.11.0/2.1.0

// sourceMappingURL comment is not included in the compressed file.