Eventsource

An spec compliant implementation of the Eventsource spec with useful extensions

What do you mean by "spec compliant"

Well, It's not currently possible to write a 100% spec compliant in javascript at the moment. There're small well-known discrepancies with the spec:

• Request initiator type cannot be "other" as stated in the spec.
• Request redirections are followed, not only 301 and 307 ones as the non normative introduction section states.
• There's no way to access to the aborted flag of a response. Due to this fact, there's no way to know whether or not an error typed response is an aborted network error one. For this reason, network errors as defined in the spec triggers an attempt to restablish the connection instead of failing the connection if the response is an aborted network error as the spec states.

Extensions

Custom headers

Like any other class, EventSource can be extended. The _buildHeaders method can be overridden in order to build custom headers:

import { EventSource, EventSourceInit } from '@cornie-js/eventsource';

class CustomEventSource extends EventSource {
  readonly #token: string | undefined;

  constructor(
    url: string,
    eventSourceInitDict: EventSourceInit & { token?: string } = {},
  ) {
    super(url, eventSourceInitDict);

    this.#token = eventSourceInitDict.token;
  }

  protected override _buildHeaders(): Headers {
    // Keep other relevant SSE headers in the base class method.
    const headers: Headers = super._buildHeaders();

    if (this.#token !== undefined) {
      headers.set('authorization', `Bearer ${this.#token}`);
    }

    return headers;
  }
}

Why not simply providing an optional headers parameter in the constructor? Well, most auth flows are way more complex than simply passing some pre established headers. As an example, JWT tokens must be renewed once the expiration time is reached.