cpfMask.js

function cpfMask(e){
  var value = e.target.value
  var separatorList = [[3, '.'], [3, '.'], [3, '-'], [2, '']]
  var clean = value.replace(/[^\d]/g, "").substr(0, 11)
  var value2 = ""
  var index = 0
  for(var i = 0; i < separatorList.length; i++){
    var separator = separatorList[i][1]
    var len = separatorList[i][0]
    value2 += clean.substr(index, len)
    index += len
    if(clean.length >= index) value2 += separator
    else break
  }
  e.target.value = value2
}

function applyCpfMask(selector){
  var input = document.querySelector(selector)
  input.placeholder="000.000.000-00"
  input.type = "text"
  input.onkeyup = cpfMask
}

// Apply
applyCpfMask('input[name=cpf]')