Braintree NodeJS

Question

在以下脚本中，我利用Braintree JS API尝试并标记其沙盒有效的信用卡信息。但是，我遇到了错误：

/..../js/braintree.js:25
          clientInstance.request({
                        ^

TypeError: Cannot read property 'request' of undefined
    at /..../js/braintree.js:25:25
    at null._onTimeout (/..../js/node_modules/braintree-web/lib/deferred.js:9:10)
    at Timer.listOnTimeout (timers.js:92:15)

表明我的clientInstance未定义。有人能帮助我注意到我所缺少的东西吗？

var createClient = require('braintree-web/client').create;


function generateNonce(generatedToken, ccnum, cccvv, ccexp, postal) {
createClient({
          authorization: generatedToken
      }, function (createErr, clientInstance) {
          var data = {
              creditCard: {
                  number: ccnum,
                  cvv: cccvv,
                  expirationDate: ccexp,
                  billingAddress: {
                      postalCode: postal
                  },
                  options: {
                      validate: false
                  }
              }
          };
          // Warning: For a merchant to be eligible for the easiest level of PCI compliance (SAQ A),
          // payment fields cannot be hosted on your checkout page.
          // For an alternative to the following, use Hosted Fields.
          clientInstance.request({
              endpoint: 'payment_methods/credit_cards',
              method: 'post',
              data: data
          }, function (requestErr, response) {
              // More detailed example of handling API errors: https://codepen.io/braintree/pen/MbwjdM
              if (requestErr) { throw new Error(requestErr); }

              console.log('Got nonce:', response.creditCards[0].nonce);
              this.onRetrieval(response.creditCards[0].nonce);
            });
        });
}

generateNonce("valid-client-token", "4111111111111111", "123", "10/20", "1337");