import { mnemonicGenerate, mnemonicToLegacySeed, mnemonicValidate } from 'https://deno.land/x/polkadot@0.2.25/util-crypto/mod.ts';

const mnemonic = mnemonicGenerate(); // => string
const isValidMnemonic = mnemonicValidate(mnemonic); // => boolean

if (isValidMnemonic) {
  console.log(`Seed generated from mnemonic: ${mnemonicToLegacySeed(mnemonic)}`); => u8a
}