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Editorial Team
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Asked: 2026-06-10T00:05:12+00:00

I’m trying to build an administration backend Rails engine. Suppose the Engine has the

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I’m trying to build an “administration backend” Rails engine. Suppose the Engine has the following assets:

ENGINE/app/assets
├── javascripts
│   └── railsyard
│       ├── admin.js.coffee
│       ├── admin_customizations.js.coffee
...

Where the admin.js.coffee is requiring admin_customizations.js.coffee, that is, an empty file ready to be overwritten by the hosting Rails application.

[ENGINE/app/assets/javascripts/my_engine/admin.js.coffee]
#= require admin_customizations
# ...some code...

[ENGINE/app/assets/javascripts/my_engine/admin_customizations.js.coffee]
# Override this empty file to add custom JS behaviour!

Everything works wonderfully, until I try to require some assets coming from a secondary gem:

[APP/app/assets/javascripts/my_engine/admin_customizations.js.coffee]
#= require modernizr # this line gets ignored
alert "Foobar"       # this line works

The gem modernizr-rails is a dependency of the hosting app rather then the engine.
Please note that if I try to require modernizr from an asset file that’s not an override of some engine asset file, everything works again.

Is there a way to fix this situation?

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1 Answer

  1. Editorial Team

    I believe I have done exactly what you describe without having the problem you say you have.

    You sure there’s not something else going on? The require line getting ignored doesn’t make much sense — sprockets should either include the required file, or raise if it can’t find it. Just silently doing nothing doesn’t seem right.

    It’s possible you’re triggering a bug in sprockets or the rails asset pipeline use of it — but more likely, there’s something else going on.

    You sure you haven’t accidentally provided your own blank ‘modernizr.js` file in the local app and/or engine, accidentally overriding the one you mean to be requiring from the modernizr gem?

    sprockets require lines do need to be in comments that preceed any code in file, they have to be in an initial prefatory comment block. could that be getting you?

    or maybe something else that’s not actually what you think it is.

    I don’t actualy use coffeescript myself, something weird with coffeescript somehow?

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