How to use the braintree-web/vault-manager.create function in braintree-web

DropinModel.prototype.initialize = function () {
  var self = this;

  return vaultManager.create({
    client: self._options.client
  }).then(function (vaultManagerInstance) {
    self._vaultManager = vaultManagerInstance;

    return getSupportedPaymentOptions(self._options);
  }).then(function (paymentOptions) {
    self.supportedPaymentOptions = paymentOptions;

    return self.getVaultedPaymentMethods();
  }).then(function (paymentMethods) {
    self._paymentMethods = paymentMethods;
    self._paymentMethodIsRequestable = self._paymentMethods.length > 0;
  });
};