Count All Valid Pickup and Delivery Options LeetCode solution in JavaScript

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var countOrders = function (n) {
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  let ans = 1; //for n=1, there will only be one valid pickup and delivery
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  for (let i = 2; i <= n; i++) {
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    let validSlots = 2 * i - 1; //calculating number of valid slots of new pickup in (n-1)th order
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    validSlots = (validSlots * (validSlots + 1)) / 2;
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    ans = (ans * validSlots) % 1000000007; //multiplying the ans of (n-1)th order to current order's valid slots
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  }
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  return ans;
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};