bible/assets/js/app.js

// Page startup.
//
// Pages arrive whole -- composed by the service worker, or by boot.html on the
// visit before there is one -- so there is nothing here that builds a page.
// What is left is the three things a composed document cannot do for itself:
// put a swapped-in page where it belongs before it is painted, land the
// reference picker where the reader asked to go, and tell the chrome when a
// worker has appeared to answer it.
//
// Three things used to live here and no longer do, all for the same reason:
// they were reading the page to work out something that was already known
// somewhere better.
//
// The reference picker was built by reading the chapters and verses off the
// book on screen. It is markup and htmx now: sw.js renders it from
// bible/verses.json and answers api/reference, and the address-bar update that
// a change event used to run through here is a response header on the answer.
// See templates/reference.njk.
//
// The verse dialog was built by scraping the book name out of article
// [data-name] and the chapter out of the enclosing section, then filling a
// form and showing it. sw.js answers api/verse with the whole of the dialog,
// htmx swaps it into the empty modal in templates/base.njk, and Bootstrap
// opens it -- which is htmx's own bootstrap-modal example, with the click
// delegated because the trigger is one of 38,000 generated verse numbers and
// cannot carry attributes of its own. See templates/verse.njk.
//
// The third was marking those numbers as controls: role, tabindex and an
// aria-label, set on every verse on load, after every swap and after every
// history restore -- a walk over a whole book, three times over, to arrive at
// the same three attributes every time. They are in the markup now, written
// by compile_bible.py, because nothing about them depends on anything only the
// browser knows. It costs the corpus a couple of megabytes and saves the pass.
(function () {
  'use strict';

  // -- events -------------------------------------------------------------

  document.body.addEventListener('htmx:afterSwap', function (event) {
    var target = event.detail.target;
    if (!target) return;
    // Both selects answer into the verse list, so this is either of them.
    if (target.id === 'reference-verse') return landOnReference();
    if (target.id === 'content') { land(); showVersion(); }
  });

  // A history restore does not go through the request pipeline -- htmx swaps
  // the element straight in and fires this instead -- so the work afterSwap
  // does has to be repeated here or a page reached by the back button arrives
  // scrolled to wherever the last one was. The picker listens for the same
  // event itself, from the navbar, because a restore reaches nothing outside
  // #content.
  document.body.addEventListener('htmx:historyRestore', function () {
    land();
    showVersion();
  });

  // -- startup ------------------------------------------------------------

  function hashTarget() {
    if (!location.hash) return null;
    return document.getElementById(decodeURIComponent(location.hash.slice(1)));
  }

  // Every scroll here is a correction, not a gesture: the page is meant to
  // arrive already in position. So they all say instant.
  //
  // Saying nothing would not mean instant. The default is "auto", which means
  // "whatever scroll-behavior computes to" -- and Bootstrap's Reboot sets
  // :root { scroll-behavior: smooth }, so the default animates. Bootstrap
  // wraps that in prefers-reduced-motion, which is the right call for the
  // chapter nav's own anchors; these are not that.
  //
  // Asked for twice, because "instant" is a later addition to an old enum and
  // a browser that does not know the value rejects the whole call with a
  // TypeError rather than ignoring the word -- so on an older WebKit this did
  // not scroll slowly, it did not scroll at all. "auto" is what the enum has
  // always had; it animates here, which is worse than instant and far better
  // than staying put.
  function jumpTo(el) {
    try {
      el.scrollIntoView({ block: 'start', behavior: 'instant' });
    } catch (err) {
      el.scrollIntoView({ block: 'start', behavior: 'auto' });
    }
  }

  // The same, for the top of the page and the same reason.
  function jumpToTop() {
    try {
      window.scrollTo({ top: 0, behavior: 'instant' });
    } catch (err) {
      window.scrollTo(0, 0);
    }
  }

  // A worker-composed page is an ordinary document and the browser scrolls to
  // the anchor itself. One composed by boot.html is not: it replaced a
  // document the browser had already finished with, so the fragment identifier
  // has been spent. Repeating it costs nothing in the first case and is what
  // makes a link to GEN#v1_1 land on the verse in the second.
  function scrollToHash() {
    var el = hashTarget();
    if (el) jumpTo(el);
  }

  // Where a swapped-in page should sit before it is ever seen.
  //
  // htmx does this itself -- scrolling to the anchor a boosted href named, or
  // to the top of the target when it named none -- but from the settle
  // callback, which is a setTimeout of defaultSettleDelay, 20ms. The browser
  // paints the new content at the old scroll offset first, so the jump is
  // visible every time. Here it runs in the same task as the swap, before any
  // paint, so the page simply appears where it belongs. htmx's own scroll
  // still follows and finds nothing left to do.
  //
  // htmx has already pushed the new URL by this point -- history is updated
  // before the swap, not after -- so location.hash is the anchor that was
  // asked for.
  function land() {
    var el = hashTarget();
    if (el) jumpTo(el);
    else jumpToTop();
  }

  // Where the reference picker lands, which is the one scroll in the app that
  // is a gesture: the reader asked for chapter 3 and is waiting to be taken
  // there.
  //
  // It used to ride along on the answer, as show: on HX-Reswap, and be htmx's
  // scroll rather than this file's. Two reasons it is here now. The smaller
  // one is that htmx's own scrollIntoView says "instant" with nothing around
  // it, so the enum above takes the whole scroll down with it. The larger one
  // is the phone: a select on iOS is a picker drawn over the page, the change
  // event arrives while it is still up, and dismissing it puts the page back
  // where it stood when it opened -- undoing anything scrolled in between.
  // The options were swapping correctly and the book never moved.
  //
  // So: once now, for a pointer, and once more after the picker has had time
  // to finish, but only if the page did not stay where it was put. That test
  // is also what keeps the second attempt from yanking back a reader who has
  // started scrolling on their own.
  //
  // The anchor comes from the address bar. The worker sends HX-Replace-Url
  // with the answer and htmx updates history before it swaps, so by the time
  // this runs location.hash is already naming the chapter or verse chosen.
  var PICKER_SETTLE_MS = 350;

  function landOnReference() {
    var el = hashTarget();
    if (!el) return;
    jumpTo(el);
    var landed = window.pageYOffset;
    setTimeout(function () {
      var again = hashTarget();
      if (again && Math.abs(window.pageYOffset - landed) > 2) jumpTo(again);
    }, PICKER_SETTLE_MS);
  }

  // The version readout, shown under the book list and nowhere else.
  //
  // It is chrome: it sits outside #content, so it outlives every swap -- and
  // so does the body class it was rendered with, which is exactly why that
  // cannot be what decides. What is in #content can, because that is the one
  // thing a swap changes: the book list is the fragment rooted at .index.
  //
  // Toggling the class rather than the style because Bootstrap declares
  // .d-none !important, which an inline display would lose to.
  //
  // Only the digest line is missing on a page boot.html composed -- there was
  // no worker to name a version -- so the element itself is always here.
  function showVersion() {
    var el = document.getElementById('app-version');
    if (!el) return;
    el.classList.toggle('d-none', !document.querySelector('#content .index'));
  }

  // api/bookmark has no origin server -- it is answered by the worker -- so
  // there is nothing to ask until the worker is controlling this page.
  // controller, not ready: ready can resolve a tick before clients.claim()
  // takes effect, and a request sent in that gap reaches the network and 404s.
  function whenControlled(fn) {
    if (!('serviceWorker' in navigator)) return;
    if (navigator.serviceWorker.controller) return fn();
    navigator.serviceWorker.addEventListener('controllerchange', fn, { once: true });
  }

  // Deferred scripts run before DOMContentLoaded fires, so this always lands,
  // and it lands after htmx has processed the shell.
  document.addEventListener('DOMContentLoaded', function () {
    scrollToHash();
    showVersion();

    // Registered from the page it is going to serve, not from a page of its
    // own: there is nothing to wait for and nothing to reload. This load is
    // already the real app -- the worker installs alongside it, and takes over
    // composing, the bookmark and the offline download from the next
    // navigation on.
    if ('serviceWorker' in navigator) {
      navigator.serviceWorker.register('sw.js').catch(function () {});
    }
    whenControlled(function () {
      document.body.dispatchEvent(new CustomEvent('worker-ready'));
    });
  });
})();