whole_func_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();
    });
  }
func_code_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();
    });
  }
func_documentation_string: camelize any string, e.g hello world -> helloWorld
  @param  {string} str only accept string!
  @return {string}     camelize string