szQocks

"postcss": "^8.4.32",
    "postcss-loader": "^7.3.4",
    "postcss-preset-env": "^9.3.0",

$result = [];

foreach ($arr as $n) {
  for ($visited = []; array_key_exists($n, $arr); $visited[] = $n, $n = $arr[$n]) {
    if (($i = array_search($n, $visited)) !== false) {
      $loop = array_slice($visited, $i);
      if (empty(array_intersect(array_column($result, 0), $loop))) {
        $result[] = $loop;
      }
      break;
    }
  }
}

$result = [];
$visited = [];
$iLoop = -1;

foreach ($arr as $n) {
  for ($iLoop++; isset($arr[$n]); $visited[$n] = $iLoop, $n = $arr[$n]) {
    if (isset($visited[$n])) {
      if ($visited[$n] === $iLoop) {
        for ($loop = [ $m = $n ]; ($m = $arr[$m]) !== $n; $loop[] = $m) ;
        $result[] = $loop;
      }
      break;
    }
  }
}

const group = (arr, key) =>
  arr.reduce((acc, n) => {
    const k = n[key];
    (acc[k] = acc[k] || []).push(n);
    return acc;
  }, {});


const result = Object.values(group(array, 'prop'));

function group(data, key, val = n => n) {
  const getKey = key instanceof Function ? key : n => n[key];
  const getVal = val instanceof Function ? val : n => n[val];
  const grouped = {};

  for (const n of data) {
    (grouped[getKey(n)] ??= []).push(getVal(n));
  }

  return grouped;
}

const groupedBySign = group([ 0, 1, 2, 3, -10, -20, -30, 0 ], Math.sign);

const groupedByParity = group(Array(10).keys(), n => [ 'чётные', 'нечётные' ][n & 1]);

const chars = group(
  'ABC123?!+',
  n =>
    n.toLowerCase() !== n.toUpperCase() ? 'буква' :
    Number.isInteger(+n)                ? 'цифра' :
                                          'другое'
);

<input name="xxx" value="69">
<input name="xxx" value="187">
<input name="xxx" value="666">
<input name="yyy" value="0">

const values = group(document.querySelectorAll('input'), 'name', 'value');

const result = Object.values(Object.groupBy(array, n => n.prop));

Какие есть способы отслеживания подключений, как это делают соцсети?

1. Использовать EAV;
   
2. Если есть возможность переехать на Postgresql - jsonb;
   

.your-image {
  pointer-events: none;
}

.your-image {
  user-select: none;
}

body {
  user-select: none;
}

body {
  -webkit-tap-highlight-color: transparent;
}

const el = document.querySelector('p');
const strings = [ 'hello, world!!', 'fuck the world', 'fuck everything' ];
const delay = 100;

function Typewriter(el, strings, delay) {
  let i = 0;
  let length = 0;

  return setInterval(() => {
    if (++length > strings[i].length) {
      i = -~i % strings.length;
      length = 0;
    }

    el.textContent = strings[i].slice(0, length);
  }, delay);
}


const intervalId = Typewriter(el, strings, delay);
// хотим остановить, делаем так: clearInterval(intervalId);

function Typewriter(el, strings, delay) {
  let timeoutId = null;

  (function step(i, length) {
    length = -~length % -~strings[i].length;
    i = (i + !length) % strings.length;
    el.innerText = strings[i].substring(0, length);
    timeoutId = setTimeout(step, delay, i, length);
  })(0, 0);

  return () => clearTimeout(timeoutId);
}


const stop = Typewriter(el, strings, delay);
// хотим остановить, делаем так: stop();

DELETE FROM A WHERE A.id NOT IN (SELECT id FROM B);

типа, антипаттерн...

но это все равно вызов метода в конструкторе, что не приветствуется.

const defaults = {
  index: 0,
  length: 0,
  step: 1,
};

function Typewriter({ strings, delay }) {
  const [ state, setState ] = useState(null);

  useEffect(() => {
    setState(() => ({...defaults}));
  }, [ strings ]);

  useEffect(() => {
    const timeoutId = setTimeout(setState, delay, ({...state}) => {
      state.length += state.step;
      if (state.length === strings[state.index].length) {
        state.step = -1;
      } else if (state.length === 0) {
        state.step = 1;
        state.index = (state.index + 1) % strings.length;
      }
      return state;
    });

    return () => clearTimeout(timeoutId);
  });

  return <div>{strings?.[state?.index]?.slice(0, state?.length)}</div>;
}