9_resolve_3.js

const resolveWithInstrumentation = (resolve) => {
  return (source, args, context, info) => {
    const directives = info.fieldASTs[0].directives;
    const instrumentDirective = directives.filter(d => d.name.value === InstrumentDirective.name)[0];
    if (!instrumentDirective) {
      return resolve(source, args, context, info);
    }

    const start = new Date();
    return Promise.resolve(resolve(source, args, context, info)).then((result) => {
      const diff = (new Date() - start);
      const tag = instrumentDirective.arguments[0].value.value;
      console.log(`Instrumented ${tag} @ ${diff}ms`)
      return result;
    });
  };
};