问在NodeJS中遇到"ReferenceError: calendar is not defined“，但在谷歌的API Test Console中也可以使用相同的代码

EN

const moment = require('moment');
const {  google } = require('googleapis');

exports.handler = function(context, event, callback) {

  // Initialize Google Calendar API
  const cal = google.calendar({
    version: 'v3',
    auth: context.GOOGLE_API_KEY
  });

  //Read Appointment Date
  let apptDate = event.ValidateFieldAnswer;

  var status = false;

  const res = {
    timeMin: moment().toISOString(),
    timeMax: moment().add(10, 'minutes').toISOString(),
    items: [{
      id: context.GOOGLE_CALENDAR_ID
    }]
  };
  console.log(res);

  cal.freebusy.query({
    resource: res
  }).then((result) => {
    const busy = result.data.calendars[calendar].busy;
    console.log("Busy: " + busy);
    if (busy.length !== 0) {
      let respObj1 = {
        "valid": false
      };
      console.log("Failed");
      callback(null, respObj1);
    } else {
      let respObj1 = {
        "valid": true
      };
      console.log("Success");
      callback(null, respObj1);
    }
  }).catch(err => {
    console.log('Error: checkBusy ' + err);
    let respObj1 = {
      "valid": false
    };
    callback(null, respObj1);
  });

};