dokaku.js

function zero(str) {
  var m
  if (m = str.match(/^0(?!\d)(.*)/)) {
    return m[1]
  }
  throw "zero"
}

function decimal(str) {
  var m

  try {
    return zero(str)
  } catch (e) {
    if (m = str.match(/^[1-9]\d*(.*)$/)) {
      return m[1]
    } else {
      throw "decimal"
    }
  }
}

function hex(str) {
  var m
  try {
    return zero(str)
  } catch (e) {
    if (m = str.match(/^[1-9a-x][0-9a-x]*(.*)$/i)) {
      return m[1]
    } else {
      throw "hex"
    }
  }
}

function machex(str) {
  var m
  if (m = str.match(/^\xhh(.*)$/)) {
    return m[1]
  } else {
    throw "machex"
  }
}

function dash(str) {
  if (m = str.match(/^-(.*)/)) {
    return m[1]
  }
  throw "dash"
}

function colon(str) {
  if (m = str.match(/^:(.*)/)) {
    return m[1]
  }
  throw "colon"
}

function dot(str) {
  if (m = str.match(/^\.(.*)/)) {
    return m[1]
  }
  return "dot"
}

try {
decimal("0123")
decimal("123:hoge")
decimal("0")
} catch (e) {
  console.log("fail", e)
}

function ipv4(str) {
  try {
    decimal(dot(decimal(dot(decimal(dot(decimal(str)))))))
    return true
  } catch (e) {
    throw "ipv4"
  }
}