Function run_a_script 

pub fn run_a_script<D, R, C>(
    cx: &mut C,
    global: &D::GlobalScope,
    f: impl FnOnce(&mut C) -> R,
) -> R
where
    C: AsMut<JSContext>,
    D: DomTypes,

Wrapper that pushes and pops entries from the script settings stack.

https://html.spec.whatwg.org/multipage/#prepare-to-run-script https://html.spec.whatwg.org/multipage/#clean-up-after-running-script