Save hashes of displayed comments locally and mark new ones when displayed for the first time
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// ==UserScript==
// @name HN: style unread content
// @description Save hashes of displayed comments locally and mark new ones when displayed for the first time
// @namespace myfonj
// @match https://news.ycombinator.com/*
// @grant none
// @version 1.0.2
// @author myfonj
// ==/UserScript==
// https://greasyfork.org/en/scripts/423969/versions/new
// Styles. Just lame green-transparent right border, for now.
const VISIBILITY_DURATION_MS = 900;
const CLASSES = { new: 'new', read: 'read', old: 'old' };
document.head.appendChild(document.createElement('style')).textContent = `
.${CLASSES.new} { border-right: 2px solid #3F36; display: block; padding-right: 1em; }
.${CLASSES.read} { border-right: 2px solid #0F03; display: block; padding-right: 1em; }
.${CLASSES.old} { /* nothing */ }
`;
const HASH_DIGEST_ALGO = 'SHA-1'; // 'SHA-256';
const MAP_EL_HASH = new WeakMap();
const MAP_EL_TIMEOUT = new WeakMap();
const LS_KEY = 'displayed_hashes_' + HASH_DIGEST_ALGO;
const SEEN_HASH_LIST = new Set((localStorage.getItem(LS_KEY) || '').split(','));
const ELS_TO_WATCH = document.querySelectorAll('.commtext,.storylink');
const ENTRY_CHECKER = (entry) => {
const TGT = entry.target;
if (entry.isIntersecting) {
if (MAP_EL_TIMEOUT.get(TGT)) {
// don't set twice on re-entry
return
}
MAP_EL_TIMEOUT.set(
TGT,
window.setTimeout(function () {
if (MAP_EL_TIMEOUT.get(TGT)) {
TGT.classList.remove(CLASSES.new);
TGT.classList.add(CLASSES.read);
SEEN_HASH_LIST.add(MAP_EL_HASH.get(TGT))
MAP_EL_TIMEOUT.delete(TGT);
VIEWPORT_OBSERVER.unobserve(TGT);
// TODO move the saving to LS to unload and/or blur for fewer writes
localStorage.setItem(
LS_KEY,
Array.from(SEEN_HASH_LIST).join(',')
);
}
}, VISIBILITY_DURATION_MS)
);
} else {
MAP_EL_TIMEOUT.delete(TGT);
}
}
const VIEWPORT_OBSERVER = new IntersectionObserver(
(entries, observer) => {
entries.forEach(_=>ENTRY_CHECKER(_));
},
{
root: null,
rootMargin: "-9%", // TODO use "lines" height here?
threshold: 0
}
);
ELS_TO_WATCH.forEach(async el => {
const hash = await makeHash(el.textContent);
if (SEEN_HASH_LIST.has(hash)) {
el.classList.add(CLASSES.old);
return;
}
el.classList.add(CLASSES.new);
MAP_EL_HASH.set(el, hash);
VIEWPORT_OBSERVER.observe(el);
});
async function makeHash (input) {
return btoa(
String.fromCharCode.apply(
null,
new Uint8Array(
await crypto.subtle.digest(
HASH_DIGEST_ALGO,
(new TextEncoder()).encode(input)
)
)
)
);
};