import { BlockNumber } from "../../types/interfaces";
import { Observable } from 'rxjs';
import { ApiInterfaceRx } from "../../api/types";
/**
 * @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(api: ApiInterfaceRx): () => Observable<BlockNumber>;