Creating a dynamic code regular expression object to match hosts.

hostregexp.js

function hostregexp(val) {
  var source = !isregexp(val)
    ? String(val).replace(escapeRegExp, escapeReplace).replace(asteriskRegExp, asteriskReplace)
    : val.source

  // force leading anchor matching
  if (source[0] !== '^') {
    source = '^' + source
  }

  // force trailing anchor matching
  if (!endAnchoredRegExp.test(source)) {
    source += '$'
  }

  return new RegExp(source, 'i')
}