Handler

A Handler is a closure wrapper. Due to how closures work, they aren't the best to work with on structs (in this case: elements). So to fix this we use a Handler which is a wrapper for the closure, Then you can safely clone and use it without any problems (in which a normal closure would fail at)

Examples

Handler::new(|btn: &mut Button, event, document| {
    // do something
})

A better way to do this is:

rsx! {
    button {
        // No need for Handler::new
        on_click: fn(btn: &mut Button, event, document) {
            // do something
        }
    }
}

fn() {} is a part of our macro rsx!. In rust you would normally use || {}