function escapeHtml (string) {
  var str = '' + string
  var match = matchHtmlRegExp.exec(str)

  if (!match) {
    return str
  }

  var escape
  var html = ''
  var index = 0
  var lastIndex = 0

  for (index = match.index; index < str.length; index++) {
    switch (str.charCodeAt(index)) {
      case 34: // "
        escape = '&quot;'
        break
      case 38: // &
        escape = '&amp;'
        break
      case 39: // '
        escape = '&#39;'
        break
      case 60: // <
        escape = '&lt;'
        break
      case 62: // >
        escape = '&gt;'
        break
      default:
        continue
    }

    if (lastIndex !== index) {
      html += str.substring(lastIndex, index)
    }

    lastIndex = index + 1
    html += escape
  }

  return lastIndex !== index
    ? html + str.substring(lastIndex, index)
    : html
}
Escape special characters in the given string of text.

@param  {string} string The string to escape for inserting into HTML
@return {string}
@public