Check Completeness of a Binary Tree LeetCode solution in JavaScript

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var isCompleteTree = function (root) {
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  let queue = [root];
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  let answer = [root];
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  while (queue.length > 0) {
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    let current = queue.shift();
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    if (current) {
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      queue.push(current.left);
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      answer.push(current.left);
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      queue.push(current.right);
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      answer.push(current.right);
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    }
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  }
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  console.log("queue", queue);
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  while (answer.length > 0) {
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    let current = answer.shift();
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    if (current === null) break;
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  }
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  console.log("answer after shifting", answer);
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  let flag = true;
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  for (let current of answer) {
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    if (current !== null) {
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      flag = false;
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      break;
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    }
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  }
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  return flag;
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};