Where does an anonymous function gets its arguments

Question

I'm learning to develop Windows 8 style applications with the help of a book. The chapter I'm reading focuses on HTML, CSS and JavaScript languages for developing. The application displays in a ListView the images you have in the My Pictures Folder and deletes them when the user clicks or taps an image. Here is the code that implements the deletion of an image in the ListView:

var lv = document.getElementById('lv');
lv.addEventListener('iteminvoked', function (eventObj) {
    eventObj.detail.itemPromise.then(function (listViewItem) {
        var binding = files.dataSource.createListBinding();
        binding.fromIndex(listViewItem.index).then(function (dataItem) {
            var key = dataItem.key;
            files.dataSource.remove(key);
            binding.release();
         });
     });
});

My question is, where does the eventObj parameter of the anonymous function in the addEventListener method gets its value? I have found a similar question asked here: Passing arguments in anonymous functions in JavaScript, but i cannot fully understand it. I searched the documentation for addEventListener on MSDN but it just says it takes an event handler function, but it doesn't say anything about the parameters. Thanks in advance.

Answer 1

Event handlers may be attached to various objects including DOM elements, document, the window object, etc. When an event occurs, an event object is created and passed sequentially to the event listeners.

Source: https://developer.mozilla.org/en-US/docs/Web/API/Event

An event listener or event handler can be an anonymous function or named function, it really doesn’t matter. The point is that it’s the event interface that defines the event object that is passed to the handler.

To find out exactly the event property from the event you are using, please refer to the windows docs: http://msdn.microsoft.com/en-us/library/windows/apps/br211827.aspx