function injectCode(code, id) {
  var pre = document.getElementById(id);
  pre.textContent = code;
  code = pre.innerHTML;
  code = prettyPrintOne(code, 'js');
  pre.innerHTML = code;
}
Inject code into a pre tag, with syntax highlighting.
Safe from HTML/script injection.
@param {string} code Lines of code.
@param {string} id ID of <pre> element to inject into.