suffix_prop_name_suffixPropName = function suffixPropName(suffix, str) {
  return str + (suffix ? upper_first(suffix) : '');
}
Suffix can be a falsey value so nothing is appended to string.
(helps when looping over props & some shouldn't change)
Use data last parameters to allow for currying.
@param {string} suffix
@param {string} str