camelize any string, e.g hello world -> helloWorld
@param  {string} str only accept string!
@return {string}     camelize string
function camelize(str, isBig) {
  return str.replace(/(^|[^a-zA-Z]+)([a-zA-Z])/g, function (match, spilt, initials, index) {
    return !isBig && index === 0 ? initials.toLowerCase() : initials.toUpperCase();
  });
}