---
"simple-statistics": patch
---

Fix `permutationsHeap` permuting the caller's array. Heap's Algorithm works by swapping elements in place, and the implementation ran those swaps directly on the argument, so `permutationsHeap([1, 2, 3])` left the caller holding `[3, 2, 1]`, the last permutation generated. Calling it twice on the same array returned two different lists, and a frozen input threw `TypeError: Cannot assign to read only property '0'`. The swaps now run on a copy, matching the defensive copying already used in `shuffle`. The returned permutations are unchanged.