docs: function compare(prop, a, b) {
    if (typeof prop === 'function') {
      // expose `compare` to custom function
      return prop(a, b, compare.bind(null, null));
    }
    // compare object values
    if (prop && typeof a === 'object' && typeof b === 'object') {
      return compare(null, get(a, prop), get(b, prop));
    }
    return defaultCompare(a, b);
  }