Maximum Binary String After Change LeetCode solution in JavaScript

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/**
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 * @param {string} binary
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 * @return {string}
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 */
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var maximumBinaryString = function (binary) {
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  /*
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    10 -> 01 allows us to move any zero to left by one position
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    00 -> 10 allows us to convert any consicutive 00 to 10
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    So we can collect all the zeros together then convert them in 1 except for the rightmost 0
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    We will club all the zeros togegher on the rightmost possition, to achieve the biggest value, then covert them into 1 except for the rightmost 0
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    So we need to choose indexOfFirstZero as the starting possition of the group of zeros
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    If there is no 0 then given string is the maximum possible string
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    If there are 1 or more zeros
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        Then there will be only 1 zero in the answer
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        Position of this will be indexOfFirstZero in given string + countOfZeros - 1
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    */
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  let firstZeroIndex = -1,
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    zeroCount = 0,
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    ans = "";
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  for (let i = 0; i < binary.length; i++) {
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    if (binary[i] === "0") {
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      zeroCount++;
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      if (firstZeroIndex === -1) {
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        firstZeroIndex = i;
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      }
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    }
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  }
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  if (firstZeroIndex == -1) {
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    return binary;
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  }
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  let onlyZeroInAns = firstZeroIndex + (zeroCount - 1);
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  for (let i = 0; i < binary.length; i++) {
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    if (i == onlyZeroInAns) {
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      ans += "0";
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    } else {
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      ans += "1";
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    }
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  }
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  return ans;
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};