safe truncate html, without broken any tags

trunc_html.js

function truncHtml(html, truncNum) {
  if (!truncNum) {
    return 0
  }
  let sum = 0, index = 0
  ;('>'+html+'<').replace(/>([^<>]*)</g, (ma, g1, offset, str) => {
    g1 = g1.trim()
    if (sum - 1 < truncNum && sum + g1.length - 1 >= truncNum) {
      index = offset + (truncNum - sum) - 1
      console.log(index, offset, sum)
    }
    sum += g1.length
    return ''
  })
  truncNum = index
  const truncated = html.substring(0, truncNum)
  const removed = html.substring(truncNum)
  const reserved = removed
    .replace(/>[^<>]*</g, '><')
    .replace(/^[^<>]*</, '<')
    .replace(/>[^<>]*$/, '>')
    .replace(/<br[/]?>/g, '')
    .replace(/<img[^>]*>/g, '')
    .replace(/<div[^>]*><\/div>/g, '')
  
  return truncated + reserved
}