class FilesAdmin(admin.ModelAdmin):
    class Media:
        js = ('blog_files.js', )

$(document).ready(function() {
    allert('Hello');
});

$ is not function.

<script type="text/javascript" src="/admin/jsi18n/"></script>
<script type="text/javascript" src="/static/admin/js/core.js"></script>
<script type="text/javascript" src="/static/admin/js/admin/RelatedObjectLookups.js"></script>
<script type="text/javascript" src="/static/admin/js/jquery.js"></script>
<script type="text/javascript" src="/static/admin/js/jquery.init.js"></script>
<script type="text/javascript" src="/static/admin/js/actions.js"></script>
<script type="text/javascript" src="/static/blog_files.js"></script>

$ = django.JQuery