Number of Ways to Separate Numbers LeetCode solution in JavaScript

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const MOD = 10 ** 9 + 7;
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var numberOfCombinations = function (num) {
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  const n = num.length;
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  const counts = Array.from({ length: n }, () => new Array(n + 1).fill(0));
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  const allSameFlag = num.split("").every((c) => c === num[0]);
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  for (let i = 0; i < n; i++) {
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    counts[i][n] = num[i] !== "0" ? 1 : 0;
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  }
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  const partialCompare = (i, j) => {
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    if (i === j || allSameFlag) {
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      return 0;
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    } else if (num[i] !== num[j]) {
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      return num[i] > num[j] ? i + 1 : -(i + 1);
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    } else if (2 * j - i === n || 2 * j - i === n - 1) {
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      for (let k = 0; k < j - i; k++) {
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        if (num[i + k] !== num[j + k]) {
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          return num[i + k] > num[j + k] ? i + k : -(i + k + 1);
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        }
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      }
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      return 0;
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    } else {
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      const idx = partialCompare(i + 1, j + 1);
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      return idx === 0 ? 0 : Math.abs(idx) - 1 >= j ? 0 : idx;
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    }
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  };
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  let ans = counts[0][n];
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  for (let j = n - 1; j > 0; j--) {
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    let k = n,
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      total = 0;
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    for (let i = 0; i < j; i++) {
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      if (num[i] !== "0") {
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        while (
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          k - j > j - i ||
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          (k - j === j - i && partialCompare(i, j) <= 0)
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        ) {
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          total = (total + counts[j][k]) % MOD;
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          k--;
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        }
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        counts[i][j] = total;
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      }
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    }
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    ans = (ans + counts[0][j]) % MOD;
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    counts.pop();
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  }
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  return ans;
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};