parse_tag_expression.js

const parseElementExpression = (str) => {
  const elements = /([\#|\.][a-zA-Z]+)/;
  const itens = str.split(elements).filter(x => x);
  const getClassOrIdNames = (idOrClass) =>
                                          itens
                                          .filter(_ => _.charAt(0) === idOrClass)
                                          .map(_ => _.slice(1));
  
  const tag = itens.filter(_ => (_.charAt(0) !== '#') && (_.charAt(0) !== '.'));
  const id = getClassOrIdNames('#');
  const classes = getClassOrIdNames('.');
  
  const attrs = {id: id, 'class': classes};
    
  return [tag, attrs];
}

const [tag, attrs] = parseElementExpression("div#hellow.xyz.abc");