MediaWiki:Common.js

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/* Any JavaScript here will be loaded for all users on every page load. */
/* Display banner on archived pages */
mw.hook('wikipage.content').add(function() {
    var cats = mw.config.get('wgCategories');
    if (cats && cats.indexOf('Your Category Name') !== -1) {
        $('.mw-parser-output').prepend(
            '<div class="category-notice">This article is archived. It is either extremely out of date or no longer relevant. </div>'
        );
    }
});