react-day-picker/src/helpers/getClassNamesForModifiers.ts

Customizable Date Picker for React

import { DayFlag, SelectionState, UI } from "../UI.js";
import type { ModifiersClassNames, ClassNames } from "../types/index.js";

export function getClassNamesForModifiers(
  modifiers: Record<string, boolean>,
  classNames: ClassNames,
  modifiersClassNames: ModifiersClassNames = {}
) {
  const modifierClassNames = Object.entries(modifiers)
    .filter(([, active]) => active === true)
    .reduce(
      (previousValue, [key]) => {
        if (modifiersClassNames[key]) {
          previousValue.push(modifiersClassNames[key as string]);
        } else if (classNames[DayFlag[key as DayFlag]]) {
          previousValue.push(classNames[DayFlag[key as DayFlag]]);
        } else if (classNames[SelectionState[key as SelectionState]]) {
          previousValue.push(classNames[SelectionState[key as SelectionState]]);
        }
        return previousValue;
      },
      [classNames[UI.Day]] as string[]
    );

  return modifierClassNames;
}