@mui/material/modern/utils/mergeSlotProps.js

Material UI is an open-source React component library that implements Google's Material Design. It's comprehensive and can be used in production out of the box.

import clsx from 'clsx';
export default function mergeSlotProps(externalSlotProps, defaultSlotProps) {
  if (!externalSlotProps) {
    return defaultSlotProps;
  }
  if (typeof externalSlotProps === 'function' || typeof defaultSlotProps === 'function') {
    return ownerState => {
      const defaultSlotPropsValue = typeof defaultSlotProps === 'function' ? defaultSlotProps(ownerState) : defaultSlotProps;
      const externalSlotPropsValue = typeof externalSlotProps === 'function' ? externalSlotProps({
        ...ownerState,
        ...defaultSlotPropsValue
      }) : externalSlotProps;
      const className = clsx(ownerState?.className, defaultSlotPropsValue?.className, externalSlotPropsValue?.className);
      return {
        ...defaultSlotPropsValue,
        ...externalSlotPropsValue,
        ...(!!className && {
          className
        }),
        ...(defaultSlotPropsValue?.style && externalSlotPropsValue?.style && {
          style: {
            ...defaultSlotPropsValue.style,
            ...externalSlotPropsValue.style
          }
        })
      };
    };
  }
  const className = clsx(defaultSlotProps?.className, externalSlotProps?.className);
  return {
    ...defaultSlotProps,
    ...externalSlotProps,
    ...(!!className && {
      className
    }),
    ...(defaultSlotProps?.style && externalSlotProps?.style && {
      style: {
        ...defaultSlotProps.style,
        ...externalSlotProps.style
      }
    })
  };
}