Check if Number Has Equal Digit Count and Digit Value LeetCode solution in JavaScript

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var digitCount = function (num) {
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  const res = [...num].filter((element, index) => {
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    const reg = new RegExp(index, "g");
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    const count = (num.match(reg) || []).length;
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    return Number(element) === count;
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  });
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  return res.length === num.length;
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};