Decode String LeetCode solution in JavaScript

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var decodeString = function (s) {
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  const stack = [];
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  for (let char of s) {
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    if (char === "]") {
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      let curr = stack.pop();
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      let str = "";
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      while (curr !== "[") {
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        str = curr + str;
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        curr = stack.pop();
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      }
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      let num = "";
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      curr = stack.pop();
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      while (!isNaN(curr)) {
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        num = curr + num;
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        curr = stack.pop();
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      }
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      stack.push(curr);
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      for (let i = 0; i < Number(num); i++) {
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        stack.push(str);
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      }
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    } else stack.push(char);
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  }
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  return stack.join("");
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};