example logo extender for Icinga Web: lib/js/LogoExtender.js make sure to load this file via the javascript.xml of a module the image is supplied via the pub directory inside a module - or better pub/images/

LogoExtender.js

(function() {
    var renderLogo = function(cb) {
        var cmp = Ext.getCmp('north-frame');
        if(!cmp) {
            cb.defer(200,this,[cb]);
        } else {
            var image = String.format('{0}/modules/MyModule/resources/images/mylogo.png', AppKit.util.Config.get("path"));

            // update main component - if necessary ("backport" from a 1.9 feature)
            // only needed when on < 1.9.0
            summary = cmp.items.first();
            if(!summary.flex) {
                summary.flex = 1;
                summary.width = undefined;
                summary.minWidth = 675;
            }

            cmp.add({
                xtype: 'panel',
                width: 200,
                flex: undefined,
                bodyCfg: {
                    style: {
                        'background-image': 'url('+image+')',
                        'background-repeat': 'no-repeat',
                        'background-position': 'center right'
                    }
                }
            });
            if(cmp.rendered) cmp.doLayout();
        }
    };
    Ext.onReady(renderLogo.createCallback(renderLogo));
})();