/**
 * Priority for callbacks that produce data, e.g. by draining their own buffer into the transport. The default.
 */
export declare const LAST_CHANCE_PRIORITY_PRODUCER = 0;
/**
 * Priority for transport batchers. They run after all producers, so whatever a producer emits on its way out is
 * still transmitted.
 */
export declare const LAST_CHANCE_PRIORITY_BATCH_FLUSH = 10;
/**
 * Priority for callbacks that send large payloads directly, bypassing the batchers. They run last: keepalive
 * requests share a body size budget, and the small batches must not lose it to a large payload.
 */
export declare const LAST_CHANCE_PRIORITY_LARGE_PAYLOAD = 20;
/**
 * Triggers the `fn` when the HTML document is getting unloaded
 * (or when it looks like it might be). Useful to flush batch activities.
 * Callbacks with a lower `priority` run first.
 */
export declare function onLastChance(fn: () => void, priority?: number): void;