vscode: ts errors in js files

• VSCode Version: latest
• OS Version: latest Sierra

This doesn’t happen when I disable the built-in TypeScript and JavaScript Language Features extension… but then I lose a bunch of functionality…

Steps to Reproduce:

1. Create new file named test.js add the following to it:

const submitEl = document.getElementById('submit');

submitEl.onclick = (event) => {
  console.log('submit');

  function KeyPress(e) {
    console.log('keypress', e)
  }
  
  document.onkeydown = KeyPress;
}

1. Why am I getting ts errors on js files?

Does this issue occur when all extensions are disabled?: Yes/No