Fraction Addition and Subtraction LeetCode solution in JavaScript

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var fractionAddition = function (expression) {
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  const fractions = expression.split(/[+-]/).filter(Boolean);
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  const operator = expression.split(/[0-9/]/).filter(Boolean);
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  expression[0] !== "-" && operator.unshift("+");
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  const gcd = (a, b) => (b === 0 ? a : gcd(b, a % b));
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  const lcm = fractions.reduce((result, fraction) => {
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    const denominator = fraction.split("/")[1];
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    return (result * denominator) / gcd(result, denominator);
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  }, 1);
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  const molecularSum = fractions.reduce((total, fraction, index) => {
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    const [molecular, denominator] = fraction.split("/");
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    const multiple = (lcm / denominator) * (operator[index] === "+" ? 1 : -1);
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    return total + molecular * multiple;
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  }, 0);
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  const resultGcd = gcd(Math.abs(molecularSum), lcm);
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  return `${molecularSum / resultGcd}/${lcm / resultGcd}`;
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};