Upload

upload.before.send

Occurs before sending the upload request to the server.
This event has event.stop method.

ArticleEditor('#entry', {
    css: '/your-article-dist-path/',
    subscribe: {
        'upload.before.send': function(event) {
            var xhr = event.get('xhr');
            xhr.setRequestHeader('X-CSRF-Token', 'your-token-value');
        }
    }
});

upload.complete

Occurs when the upload complete.

ArticleEditor('#entry', {
    css: '/your-article-dist-path/',
    subscribe: {
        'upload.complete': function(event) {
            ...
        }
    }
});

upload.error

Occurs when the autosave request fails.

ArticleEditor('#entry', {
    css: '/your-article-dist-path/',
    subscribe: {
        'upload.error': function(event) {
            ...
        }
    }
});

Here is the example of JSON error response:

{
    "error": true,
    "message": "Something went wrong..."
}