Web: step snapping ignores minimumValue #840

• Platform: web (react-native-web)
• @react-native-community/slider: 5.2.1 (also current main)

Description

On web, the slider rounds the touched value to the nearest multiple of step counted from 0, not from minimumValue. If minimumValue is not a multiple of step, the reported values fall outside the step grid.

With minimumValue={1}, maximumValue={10} and step={2}:

• Expected values: 1, 3, 5, 7, 9 (as on iOS and Android).
• Actual values from the web component: multiples of 2 (plus 1 and 10 at the track ends). Releasing a quarter of the way along the track reports 4 instead of 3.

The cause is in getValueFromNativeEvent in package/src/RNCSliderNativeComponent.web.tsx:

const valueAfterStep = step
  ? Math.round(newValue / step) * step
  : newValue;

iOS uses minimumValue + round((value - minimumValue) / step) * step (package/ios/RNCSlider.m).

Reproducible demo

Render the web component with minimumValue={1}, maximumValue={10} and step={2} in a Jest test with @testing-library/react-native, fire responderRelease with pageX at a quarter of the track width, and read the value passed to onRNCSliderSlidingComplete: it is 4, not 3.