Linked List Cycle II LeetCode solution in JavaScript

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var detectCycle = function (head) {
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  let slowRunner = head;
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  let fastRunner = head;
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  while (fastRunner) {
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    fastRunner = fastRunner.next?.next;
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    slowRunner = slowRunner.next;
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    if (fastRunner === slowRunner) {
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      fastRunner = slowRunner;
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      slowRunner = head;
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      while (slowRunner !== fastRunner) {
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        slowRunner = slowRunner.next;
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        fastRunner = fastRunner.next;
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      }
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      return slowRunner;
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    }
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  }
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  return null;
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};