javascript - calling addEventListener without a DOM element -

i see salesforce lightning code calling addeventlistener without dom element , couldn't figure out doing.

1) why there not dom element before addeventlistener ? 2) purpose of '({' , '})' here ?

({     doinit: function(component, event, helper) {         //listen iframe's message         addeventlistener("message",            function(event) {             if(event.data.type === 'ready' && component.find("vfiframe")) {//iframe loaded                 component.iframeready = true;                   } else if(event.data.type === 'response') {//send response                 var cmpevt = component.getevent("response");                 cmpevt.setparams({ "data" : event.data.response});                 cmpevt.fire();             }           },          false);     },     makerequest : function(component, event, helper) {        helper.makerequest(component, event);      } })