Styled components variant and iif.

styled.ts

export const iif = <PROPS extends unknown, PROP_NAME extends keyof PROPS>(
  prop: PROP_NAME,
  val?: PROPS[PROP_NAME]
) => (propsInner: PROPS) => {
  if (val !== undefined) return propsInner[prop] === val ? "&" : "&.__NEVER";
  return propsInner[prop] ? "&" : "&.__NEVER";
};

export const variant = <PROPS extends unknown>(
  prop: PROPS[keyof PROPS],
  propName?: keyof PROPS
) => (propsInner: PROPS) => {
  // @ts-ignore
  return propsInner[propName || "variant"] === prop ? "&" : "&.__NEVER";
};