Given two integers representing the numerator and denominator of a fraction, return the fraction in string format. If the fractional part is repeating, enclose the repeating part in parentheses. If multiple answers are possible, return any of them.

fractionToDecimal.js

/**
 * @param {number} numerator
 * @param {number} denominator
 * @return {string}
 */
var fractionToDecimal = function(numerator, denominator) {
    if (numerator === 0) return "0";

    let result = "";

    // Handle negative signs
    if ((numerator < 0) ^ (denominator < 0)) result += "-";

    // Convert to absolute values to simplify
    let num = Math.abs(numerator);
    let den = Math.abs(denominator);

    // Append the integer part
    result += Math.floor(num / den);
    let remainder = num % den;

    if (remainder === 0) return result;

    result += ".";

    // Map to store previously seen remainders and their positions
    let map = new Map();
    while (remainder !== 0) {
        if (map.has(remainder)) {
            // Insert parentheses around the repeating part
            let index = map.get(remainder);
            result = result.slice(0, index) + "(" + result.slice(index) + ")";
            break;
        }

        map.set(remainder, result.length);
        remainder *= 10;
        result += Math.floor(remainder / den);
        remainder %= den;
    }

    return result;
};