src/language-js/printer-estree.js/printDirective
function printDirective(node, options) {
  const raw = rawText(node);
  const rawContent = raw.slice(1, -1);

  // Check for the alternate quote, to determine if we're allowed to swap
  // the quotes on a DirectiveLiteral.
  if (rawContent.includes('"') || rawContent.includes("'")) {
    return raw;
  }

  const enclosingQuote = options.singleQuote ? "'" : '"';

  // Directives are exact code unit sequences, which means that you can't
  // change the escape sequences they use.
  // See https://github.com/prettier/prettier/issues/1555
  // and https://tc39.github.io/ecma262/#directive-prologue
  return enclosingQuote + rawContent + enclosingQuote;
}