The purpose of starting an initial comment with /*! in JavaScript and CSS files

Question

I've noticed that initial comment in JavaScript or CSS files is sometimes started with /*!. What is the purpose of the explanation mark?

For example, jQuery:

/*! jQuery v1.7.1 jquery.com | jquery.org/license */

Bootstrap:

/*!
 * Bootstrap v2.0.1
 *
 * Copyright 2012 Twitter, Inc

Ollie Bennett · Accepted Answer · 2013-06-23 18:12:34Z

66

It tells compression tools such as the YUICompressor and Uglify, which minify the code, to leave the commented section in place as they usually remove all comments from the code.

edited Jun 23, 2013 at 18:12

Ollie Bennett

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answered Jun 28, 2012 at 15:56

Phil Parsons

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4 Comments

Kevin Over a year ago

Is there a way to override this without removing the !? I'm using Uglify and I need to remove all blocks so I can inject the CSS file into my HTML.

Asfand Qazi Over a year ago

Of course, the point of leaving these comments in, usually, is because they are licensing messages that are required to be included with any distributed versions of the code.

keaukraine Over a year ago

Licenses are meant to be always present with code so you may violate some rights by removing them.

Peter Mortensen Over a year ago

Now deprecated?

Wallace Sidhrée · Accepted Answer · 2013-09-20 08:15:34Z

4

Some software like Coda also support the "bookmark syntax" shown below, so that one can navigate to different parts of code through the app's code navigator.

// !bookmark
/* !bookmark */
<!-- !bookmark -->

Note that in the examples above there's a space between the comment syntax the exclamation mark.

answered Sep 20, 2013 at 8:15

Wallace Sidhrée

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Comments

Peter Mortensen · Accepted Answer · 2023-09-12 13:50:23Z

4

I believe one purpose of the exclamation point is to tell JavaScript minifiers to leave these particular comments in, when condensing the files.

edited Sep 12, 2023 at 13:50

Peter Mortensen

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answered Jun 28, 2012 at 15:57

KP.

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Comments

Mike Casan Ballester · Accepted Answer · 2017-08-31 19:04:17Z

0

It is also important for attribution for the author of external dependencies/API, especially free ones.

When minifying, the least we can do is to offer them some bytes of recognition.

e.g. /*! PhotoSwipe main CSS by Dmitry Semenov | photoswipe.com | MIT license */ will not be erased by minifier.

answered Aug 31, 2017 at 19:04

Mike Casan Ballester

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