Not sure if v8 staging features are covered, but when using deno run --v8-flags=--js-base-64 or node --js-base-64 or chrome://flags/#enable-javascript-harmony, the following code gives wrong output:

// foo.ts, run with:
// deno run --v8-flags=--js-base-64 foo.ts

import 'https://deno.land/x/corejs@v3.43.0/index.js'

console.log(new Uint8Array(8).fill(255).toHex()) // gives VfVfVfVfVfVfVfVf

Solution can be adding a check similar to:

From denoland/deno#25051 (comment)