How to use 'longest palindromic substring javascript' in JavaScript

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function longestCommonPrefix(arr = []) {
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  const cnt = arr.length;
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  if (cnt === 0) return '';
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  if (cnt === 1) return arr[0];
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  const first = arr[0];
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  // complexity: O(m * n)
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  for (var m = 0; m < first.length; m++) {
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    const c = first[m];
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    for (var n = 1; n < cnt; n++) {
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      const entry = arr[n];
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      if (m >= entry.length || c !== entry[m]) {
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        return first.substring(0, m);
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      }
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    }
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  }
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  return first;
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}

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function longestCommonPrefix2(strs) {
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  const s = strs[0] || '';
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  let l = strs.length;
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  if (l <= 1) {
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    return s;
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  }
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  let min = Infinity;
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  while (l-- > 1 && min) {
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    min = Math.min(getPrefixLength2(strs[l], strs[l - 1]), min);
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  }
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  return s.substr(0, min);
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}