Minimum Remove to Make Valid Parentheses LeetCode solution in JavaScript

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var minRemoveToMakeValid = function (s) {
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  let validity = 0;
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  for (let index = 0; index < s.length; index++) {
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    if (s[index] == ")") {
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      if (validity == 0) {
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        s = s.substring(0, index) + s.substring(index + 1);
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        index--;
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      } else {
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        validity--;
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      }
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    } else if (s[index] == "(") {
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      validity++;
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    }
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  }
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  if (validity > 0) {
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    for (let index = s.length - 1; index >= 0; index--) {
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      if (s[index] == "(") {
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        s = s.substring(0, index) + s.substring(index + 1);
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        validity--;
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        if (validity === 0) break;
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      }
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    }
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  }
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  return s;
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};