'use strict'; module.exports = function (str, sep) { if (typeof str !== 'string') { throw new TypeError('Expected a string'); } sep = typeof sep === 'undefined' ? '_' : sep; return str .replace(/([a-z\d])([A-Z])/g, '$1' + sep + '$2') .replace(/([A-Z]+)([A-Z][a-z\d]+)/g, '$1' + sep + '$2') .toLowerCase(); };