Number of Digit One LeetCode solution in JavaScript

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var countDigitOne = function (n) {
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  if (n <= 0) return 0;
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  if (n < 10) return 1;
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  var base = Math.pow(10, n.toString().length - 1);
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  var answer = parseInt(n / base);
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  return (
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    countDigitOne(base - 1) * answer +
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    (answer === 1 ? n - base + 1 : base) +
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    countDigitOne(n % base)
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  );
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};