Lambda Server-Timing Middleware

Enables Lambdas to return responses with Server-Timing Header allowing to to pass request-specific timings from the backend to the browser.

Allows a server to communicate performance metrics about the request-response cycle to the user agent. It also standardizes a JavaScript interface to enable applications to collect, process, and act on these metrics to optimize application delivery.

Install

$ npm install lambda-server-timing

Usage

$ withServerTimings()

This will attach a Server-Timing header to your response headers with the timings recorded for requests.

The header looks like:

HTTP/1.1 200 OK

Server-Timing: db;dur=53, app;dur=47.2

And once succesfully returned as a response header, it is shown in the Timings tab under Networks in the Chrome Devtools. The visual example of it looks like:

This now enables developers to look throught the performance problems of their apps for not just the frontend and but also the backend.

The package also exposes the timer methods startTime and endTime so you can measure your methods on a regular basis and improve accordingly.

Usage - startTime/endTime

$ startTime('abbr', "getAbbreviatedResponse");
$ getAbbreviatedResponse({
        ...
   });
$ endTime('abbr', "getAbbreviatedResponse");

Usage - trackTime (async helper)

trackTime wraps any sync or async function, automatically recording its duration as a Server-Timing metric. It returns the function's result directly.

import { trackTime } from 'lambda-server-timing';

// Time an async database query
const user = await trackTime('db-query', async () => {
  return await dynamodb.get({ TableName: 'users', Key: { id } }).promise();
}, 'Fetch user from DynamoDB');

// Time an external API call
const data = await trackTime('external-api', async () => {
  const res = await fetch('https://api.example.com/data');
  return res.json();
});

// Also works with sync functions
const result = trackTime('compute', () => {
  return heavyComputation(input);
}, 'Heavy computation');

If the wrapped function throws an error, trackTime still records the timing before re-throwing, so you get visibility into failed operations too.