use fmt;
/// A wrapper for passing `FnMut` callbacks into the `js!` macro.
///
/// Just like when passing regular `Fn` callbacks, don't forget
/// to `drop()` them on the JavaScript side or else the closure
/// will be leaked.
///
/// # Examples
///
/// ```rust
/// let mut count = 0;
/// let callback = move || {
/// count += 1;
/// println!( "Callback called {} times", count );
/// };
/// js! {
/// var cb = @{Mut(callback)};
/// cb();
/// cb();
/// cb();
/// cb.drop();
/// }
/// ```
;