code: function save (str, isString) {
    var i = saved.length
    saved[i] = isString
      ? str.replace(newlineRE, '\\n')
      : str
    return '"' + i + '"'
  }
docs: Save replacer
  
  The save regex can match two possible cases:
  1. An opening object literal
  2. A string
  If matched as a plain string, we need to escape its
  newlines, since the string needs to be preserved when
  generating the function body.
  
  @param {String} str
  @param {String} isString - str if matched as a string
  @return {String} - placeholder with index