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);
}
})