DI String Match LeetCode solution in JavaScript

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var diStringMatch = function (s) {
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  let i = 0,
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    d = s.length,
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    arr = [];
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  for (let j = 0; j <= s.length; j += 1) {
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    if (s[j] === "I") arr.push(i++);
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    else arr.push(d--);
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  }
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  return arr;
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};