An example of making calls and handling retries when 429 responses are detected in Node.JS

nexmo-call-with-retry.js

var Nexmo = require('../lib/Nexmo');

var nexmo = new Nexmo({
    apiKey: config.API_KEY, 
    apiSecret: config.API_SECRET,
    applicationId: config.APP_ID,
    privateKey: config.PRIVATE_KEY
  },
  {debug: config.DEBUG}
);

function callWithRetry(callRequest, callback, maxRetries, retryCount) {
  retryCount = retryCount || 0;

  nexmo.calls.create(callRequest, function(error, result) {
      console.log('----------------------------');
      console.log('call response returned');
      console.log('error', JSON.stringify(error, null, 2));
      console.log('result', JSON.stringify(result, null, 2));

      if(error && error.statusCode === 429 && retryCount <= maxRetries) {
        console.log('429 detected. Retrying after', error.headers['retry-after'], 'ms');
        setTimeout(function() {
          callWithRetry(callRequest, callback, maxRetries, ++retryCount);
        }, error.headers['retry-after']);
        
      }
      else {
        callback(error, result);
      }
    });
}

const callsToMake = [
  {
    to: [{
      type: 'phone',
      number: config.TO_NUMBER
    }],
    from: {
      type: 'phone',
      number: config.FROM_NUMBER
    },
    answer_url: ['https://nexmo-community.github.io/ncco-examples/first_call_talk.json'],
    event_url: ['http://requestb.in/wgapg3wg?to=' + config.TO_NUMBER]
  },
  {
    to: [{
      type: 'phone',
      number: config.ALT_TO_NUMBER
    }],
    from: {
      type: 'phone',
      number: config.FROM_NUMBER
    },
    answer_url: ['https://nexmo-community.github.io/ncco-examples/first_call_talk.json'],
    event_url: ['http://requestb.in/wgapg3wg?to=' + config.ALT_TO_NUMBER]
  }
];

const results = [];
function makeNextCall(error, result) {
  if(error || result) {
    results.push({error: error, result: result});
  }

  if(callsToMake.length > 0) {
    var callRequest = callsToMake.shift();
    callWithRetry(callRequest, makeNextCall, 1);
  }
  else {
    console.log('--------------------------');
    console.log('all calls completed', results);
    console.log('--------------------------');
    callback(null, results);
  }
}

makeNextCall();