import { concat } from "https://deno.land/std@0.223.0/bytes/concat.ts";

const a = new Uint8Array([0, 1, 2]);
const b = new Uint8Array([3, 4, 5]);
concat([a, b]); // Uint8Array(6) [ 0, 1, 2, 3, 4, 5 ]