@mui/core/modern/composeClasses/composeClasses.js

Unstyled React components with which to implement custom design systems.

export default function composeClasses(slots, getUtilityClass, classes) {
  const output = {};
  Object.keys(slots).forEach( // `Objet.keys(slots)` can't be wider than `T` because we infer `T` from `slots`.
  // @ts-expect-error https://github.com/microsoft/TypeScript/pull/12253#issuecomment-263132208
  slot => {
    output[slot] = slots[slot].reduce((acc, key) => {
      if (key) {
        if (classes && classes[key]) {
          acc.push(classes[key]);
        }

        acc.push(getUtilityClass(key));
      }

      return acc;
    }, []).join(' ');
  });
  return output;
}