util.js

function makeMap (str, expectsLowerCase) {
  const map = Object.create(null)
  const list = str.split(',')
  for (let i = 0; i < list.length; i++) {
    map[list[i]] = true
  }
  return expectsLowerCase
    ? val => map[val.toLowerCase()]
    : val => map[val]
}

module.exports = {
  isUnaryTag: makeMap(
    'image,area,base,br,col,embed,frame,hr,img,input,isindex,keygen,' +
    'link,meta,param,source,track,wbr'
  )
}