Check Array Formation Through Concatenation LeetCode solution in JavaScript

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var canFormArray = function (arr, pieces) {
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  let total = "";
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  arr = arr.join("");
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  for (let i = 0; i < pieces.length; i++) {
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    pieces[i] = pieces[i].join("");
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    total += pieces[i];
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    if (arr.indexOf(pieces[i]) == -1) return false;
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  }
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  return total.length == arr.length;
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};