MediaWiki:Common.js

function CustomizeModificationsOfSidebar() {
    var toolbar = document.getElementById('p-tb');
    toolbar.parentNode.removeChild(toolbar);
    var node1 = document.getElementById('p-recentchanges');
    node1.parentNode.removeChild(node1);
    var node2 = document.getElementById('p-help');
    node2.parentNode.removeChild(node2);
}

if ( mw.config.get( 'wgUserId') == null ) {
    jQuery( CustomizeModificationsOfSidebar );
}