User:Enterprisey/up-one-lvl-kbd.js

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$( function() {
    var breadcrumbEl = document.getElementsByClassName( "subpages" )[0];
    if( breadcrumbEl ) {
        mw.loader.using( [ "mediawiki.util" ], function () {

            // If someone's already using the "U" access key, clear that
            var hasOurAccessKey = document.querySelectorAll( "a[accesskey=u]" );
            for( var i = 0; i < hasOurAccessKey.length; i++ ) {
                hasOurAccessKey[i].setAttribute( "accesskey", "" );
                $( hasOurAccessKey[i] ).updateTooltipAccessKeys();
            }

            var lastSubpage = breadcrumbEl.children[ breadcrumbEl.children.length - 1 ];
            lastSubpage.accessKey = "u";
            $( lastSubpage ).updateTooltipAccessKeys();
        } );
    }
} );