Clone Graph LeetCode solution in JavaScript

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var cloneGraph = function (node) {
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  if (!node) return node;
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  let queue = [node];
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  let map = new Map();
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  //1. Create new Copy of each node and save in Map
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  while (queue.length) {
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    let nextQueue = [];
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    for (let i = 0; i < queue.length; i++) {
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      let n = queue[i];
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      let newN = new Node(n.val);
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      if (!map.has(n)) {
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        map.set(n, newN);
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      }
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      let nei = n.neighbors;
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      for (let j = 0; j < nei.length; j++) {
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        if (map.has(nei[j])) continue;
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        nextQueue.push(nei[j]);
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      }
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    }
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    queue = nextQueue;
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  }
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  queue = [node];
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  let seen = new Set();
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  seen.add(node);
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  //2. Run BFS again and populate neighbors in new node created in step 1.
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  while (queue.length) {
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    let nextQueue = [];
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    for (let i = 0; i < queue.length; i++) {
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      let n = queue[i];
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      let nei = n.neighbors;
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      let newn = map.get(n);
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      for (let j = 0; j < nei.length; j++) {
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        newn.neighbors.push(map.get(nei[j]));
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        if (!seen.has(nei[j])) {
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          nextQueue.push(nei[j]);
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          seen.add(nei[j]);
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        }
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      }
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    }
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    queue = nextQueue;
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  }
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  return map.get(node);
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};