A getPriority callback is called on all outstanding requests whenever a slot frees up, allowing the application to reprioritize or even cancel "issued" requests if the application state has changed.

Note: The request scheduler does not actually issue requests, it just lets apps know when the request can be issued without overwhelming the connection and the server.

A primary use case is to let the app reprioritize or cancel requests if circumstances change before the request can be scheduled.

Some information on browser request throttling

Usage

To schedule a request so that it can be issued at a time when it can be immediately processed.

const URL = '...';
const requestToken = await requestScheduler.scheduleRequest(URL);
if (requestToken) {
  await fetch(URL);
  requestToken.done(); // NOTE: **must** be called for the next request in queue to resolve
}

Methods

constructor(options?: object)

id?: string;
throttleRequests?: boolean;
maxRequests?: number;

scheduleRequest(handle: any, getPriority?: () => number): Promise<{done: () => any)}>;

Called by an application that wants to issue a request, without having it deeply queued by the browser

When the returned promise resolved, it is OK for the application to issue a request. The promise resolves to an object that contains a done method. When the application's request has completed (or failed), the application must call the done function

Parameters

handle an arbitrary handle to identify the request, e.g. a URL string
getPriority will be called when request "slots" open up, allowing the caller to update priority or cancel the request Highest priority executes first, priority < 0 cancels the request

Returns a promise that

resolves to an object (with a done field) when the request can be issued without queueing. The application should issue the request and call done() when completed.
resolves to null if the request has been cancelled (by the callback return < 0). In this case the application should not issue the request.

About Request Priorities

The getPriority callback controls priority of requests and also cancellation of outstanding requests.