Transports let you change the way in which events are delivered to Sentry.

The JavaScript SDK uses a transport to send events to Sentry. On modern browsers, most transports use the browsers' fetch API to send events. Transports will drop an event if it fails to send due to a lack of connection.

You can change the transport by setting the transport option in the init call. The SDK provides a few built-in transports, and you can also create your own.

The makeBrowserOfflineTransport transport is a built-in transport that uses the IndexedDB API to store events when the browser is offline. When the browser comes back online, the transport sends the stored events to Sentry. Read more about how to use it.

You can also provide a custom transport to Sentry. The transport must conform to the Transport interface:

interface Transport {
  send(request: Envelope): Promise<TransportMakeRequestResponse>;
  flush(timeout?: number): Promise<boolean>;

You can also use the createTransport utility from @sentry/core to help with some boilerplate:

import { createTransport } from '@sentry/core';
import * from '@sentry/browser';

function makeFetchTransport(
): Transport {
  function makeRequest(request) {
    const requestOptions: RequestInit = {
      body: request.body,
      method: 'POST',
      referrerPolicy: 'origin',
      headers: options.headers,

    return fetch(options.url, requestOptions).then(response => {
      return {
        statusCode: response.status,
        headers: {
          'x-sentry-rate-limits': response.headers.get('X-Sentry-Rate-Limits'),
          'retry-after': response.headers.get('Retry-After'),

  return createTransport(options, makeRequest);

  dsn: '',
  transport: makeFetchTransport
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