Adding Spaces to a String LeetCode solution in JavaScript

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/**
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 * @param {string} s
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 * @param {number[]} spaces
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 * @return {string}
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 */
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var addSpaces = function (s, spaces) {
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  let words = spaces.map((space, index) =>
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    s.slice(index == 0 ? 0 : spaces[index - 1], space)
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  );
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  words.push(s.slice(spaces[spaces.length - 1]));
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  return words.join(" ");
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};