import type { ApiInterfaceRx } from '@polkadot/api/types';
import type { BlockNumber } from '@polkadot/types/interfaces';
import type { Observable } from '@polkadot/x-rxjs';
/**
 * @name bestNumber
 * @returns The latest block number.
 * @example
 * <BR>
 *
 * ```javascript
 * api.derive.chain.bestNumber((blockNumber) => {
 *   console.log(`the current best block is #${blockNumber}`);
 * });
 * ```
 */
export declare function bestNumber(instanceId: string, api: ApiInterfaceRx): () => Observable<BlockNumber>;