Function inview

explainshell/web/static/js/es.js:1135–1142

(viewtop, viewbottom, el)

}

function inview(viewtop, viewbottom, el) {
    const rect = el.getBoundingClientRect();
    const elemmiddle = rect.top + window.scrollY + rect.height / 2;

    // we consider the element to be in view when its middle is
    // within the viewport
    return viewtop < elemmiddle && viewbottom > elemmiddle;
}

function drawvisible() {
    let viewtop = window.scrollY;