calling addEventListener without a DOM element

Question

I see some salesforce lightning code that is calling addEventListener without DOM element and couldn't figure out what it is doing.

1) why there is not DOM element before this addEventListener ? 2) what the purpose of '({' and '})' here ?

({
    doInit: function(component, event, helper) {
        //listen to 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); 
    }
})