How do I get the context Menu "oncreate" Event - google-chrome

Question

I write a Chrome extension. This extension should add items to the Chrome context menü if a text is selected. This should happen dynamically everytime the contextmenu is opened.
As on this image:
The Problem:
I can't find any event that is triggered (and works) if the contextmenu opens. The following code sample doesn't work.
window.addEventListener('contextmenu', function(){
DynamicMenu.generateMenu(window.getSelection());
});
It's also impossible to trigger the adding of dynamic items from the "test" item:
chrome.contextMenus.create(
{
"title": "test",
"contexts" :["selection"],
"onclick" : DynamicMenu.generateMenu
});
Thanks for your help!
Update (how it now works):
Manifest:
...
"content_scripts": [
{
"matches": ["http://*/*", "https://*/*"],
"js": ["document_event.js"],
"run_at" : "document_idle"
}
],
...
document_event.js:
window.addEventListener('mousedown', function(e) {
var rightclick;
if (!e) var e = window.event;
if (e.which) rightclick = (e.which == 3);
else if (e.button) rightclick = (e.button == 2);
if(rightclick){
var searchText = window.getSelection().toString();
chrome.extension.sendRequest({search: searchText}, function(response) {
...
});
}
});
content.js
...
chrome.extension.onRequest.addListener(
function(request, sender, sendResponse) {
var a = request.search;
...
sendResponse({});
});
...

Answer 1

UPDATE: contextMenu onCreate Event
It's less of an official event per se, as it is a simple async callback built into the chrome.extension.create() method signature:
[integer|string] chrome.contextMenus.create(objectcreateProps,function cb)
Parameters:
REQUIRED: an object representing optional createProperties. All the properties are optional, but, the createProperties object itself is required as the first parameter to the create() method. So, if you don't want to use an custom options/properties, simply supply an empty object {}
OPTIONAL: a function which it callbacks when the create() method completes.
Return Value:
Either:
an auto-generated integer if you do not provide an id property in the createProperties object parameter when calling the method.
a string representing the generatedId of the context menu/menu item. A string is only returned if you supplied one in the createProperties object parameter when you called the create() method, and if successfully created, the string you supplied will be the EXACT VALUE that is returned.
The latest docs for the chrome.contextMenus.create API are here:
https://developer.chrome.com/extensions/contextMenus#create
.
In your case/example, you should modify your code like so:
var gId; //the id that is generated if the menu is created successfully
gId = chrome.contextMenus.create(
{//start createProperties
"title": "test",
"contexts" :["selection"],
"onclick" : DynamicMenu.generateMenu
},//end createProperties
function cmItmCreated_handler(){ //your callback (create event, if you will)
if (typeof chrome.runtime.lastError === "undefined") {
console.log("context menu/item created. 'gId' var contains generated id");
}
else {
console.error(chrome.runtime.lastError);
}
}//end function cmItmCreated_handler()
);

Answer 2

Have you tried tracking the right click event? The chrome extension context menu APIs mostly deal with clicks on the new context menu items.