v6.5.0 introduced a breaking change to turf.mask: it now mutates the mask input #2634
Description
On version v6.5.0, turf.mask(polygon, mask) now mutates mask in place. In version v6.3.0, it did not.
Since this change is not documented, it can lead to some hard-to-diagnose bugs.
Here's a simple test to verify:
const poly1 = turf.polygon([[[-73.2, 42],[-73.2, 42.2],[-73, 42.2],[-73, 42],[-73.2, 42]]]);
const poly2 = turf.polygon([[[-73.1, 42],[-73.1, 42.2],[-73.3, 42.2],[-73.3, 42],[-73.1, 42]]]);
const poly2Clone = turf.clone(poly2);
const _masked = turf.mask(poly1, poly2);
console.assert(turf.booleanEqual(poly2, poly2Clone)); // passes on v6.3.0, fails on v6.5.0This is due to the changes in #2130, which rewrote turf.mask().
The simplest solution is probably to add a mutate option and default it to false (like turf-simplify does). I'll make a PR with that approach.