/**
 * @name mnemonicGenerate
 * @summary Creates a valid mnemonic string using using [BIP39](https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki).
 * @example
 * <BR>
 *
 * ```javascript
 * import { mnemonicGenerate } from '@polkadot/util-crypto';
 *
 * const mnemonic = mnemonicGenerate(); // => string
 * ```
 */
export declare function mnemonicGenerate(numWords?: 12 | 15 | 18 | 21 | 24, onlyJs?: boolean): string;