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Targeted, backend-initiated actions can be triggered from event handlers, using methods of state. Internally, this is achieved using Framework’s mail, ephemeral state that is cleared when it reaches the intended user.

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Triggering a file download

The file_download method takes the data and file_name arguments. The first must contain raw bytes (a bytes object) or a packed file. As mentioned in the Application State section of the guide, a packed file is obtained using the wf.pack_file or wf.pack_bytes methods. 
def handle_file_download(state):
    # Pack the file as a FileWrapper object
    data = wf.pack_file("assets/story.txt", "text/plain")
    file_name = "thestory.txt"
    state.file_download(data, file_name)

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Adding a notification

Notifications Framework adds notifications when a runtime error takes place. You can add your own notifications using the add_notification method, which takes the type, title and message arguments. type must be one of error, warning, info, success. 
def notify_of_things_that_happened(state):
    state.add_notification("error", "An Error", "Something bad happened.")
    state.add_notification("warning", "A Warning", "Be aware that something happened.")
    state.add_notification("info", "Some Info", "Something happened.")
    state.add_notification("success", "A Success", "Something good happened.")

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Opening a URL

Open a URL in a new tab using the open_url method, which takes the url argument. 
def handle_open_website(state):
    state.open_url("https://writer.com")
The URL will be safely opened with noopener and noreferrer options.
Popup blockers: Given that the URL is opened asynchronously, popup blockers will likely block the new window —unless the user has opted in.

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Changing the active page

The active page and route parameters can be changed using the methods set_page and set_route_vars. This is explained in more detail in Page Routes.