GeezerVison

The modulo() helper in lib/internal/webidl.js is documented to implement ECMA-262's "x modulo y" (result has the same sign as y), but it used the JS % operator directly, whose result takes the sign of x. convertToInt step 10 relies on modulo(x, 2^bitLength) producing a non-negative representative in [0, 2^bitLength); step 11 only handles the signed upper half, so negative results of % were returned unchanged.

As a result, negative inputs to unsigned WebIDL integer types returned the original negative value instead of the two's-complement wrap (e.g. convertToInt('v', -3, 8) returned -3 instead of 253), and signed inputs in the one-wrap band below the lower bound were returned as-is (convertToInt('v', -200, 8, { signed: true }) returned -200 instead of 56). This diverged from typed-array coercion.