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README.md

Introduction

npm version

amp-optimizer-express is an express middleware that optimizes page load times for websites using AMP for their canonical pages. The middleware uses the same server-side-rendering optimizations as the Google AMP Cache.

The middleware uses the amp-optimizer component to apply server-side-rendering on the fly.

How it works

amp-optimizer-express intercepts the responses and replaces their content with a version that has been transformed by amp-optimizer.

As the server-side-rendered version of the content is not valid AMP, the component also provides the original content on an alternative URL. Server-side-rendering transformations are not applied to this URL, and the original valid AMP is served.

An AMPHTML link tag is added to the server-side-rendered version, linking it to the original valid AMP version hosted on the alternative URL.

Example:

A valid AMP page is served on https://example.com/index.html.

When the amp-optimizer-express middleware is used, that URL will serve the server-side-rendered version of the content.

The original, valid AMP will then become available at https://example.com/index.html?amp.

An amphtml link will be added to the server-side-rendered version:

<link rel="amphtml" href="https://example.com/index.html?amp">

Usage

Install via:

$ npm install @ampproject/toolbox-optimizer-express

The AMP Optimizer Middleware can be used like any other express middleware.

It is important that the middleware is used before the middleware or route that renders the page.

The example bellow will transform HTML being loaded by express-static:

const express = require('express');
const path = require('path');
const app = express();
const AmpOptimizerMiddleware = require('@ampproject/toolbox-optimizer-express');

// It's important that the AmpOptimizerMiddleware is added *before* the static middleware.
// This allows us to replace the parts needed before static handles the request.
app.use(AmpOptimizerMiddleware.create());

const staticMiddleware = express.static(path.join(__dirname, '/public'));
app.use(staticMiddleware);

Options

The following options are supported:

  • runtimeVersion: true if the optimizer should use versioned runtime imports (default is false).
  • ampOnly: true if the optimizer should only be applied to AMP files (indicated by the lightning bolt in the header).

Example:

app.use(AmpOptimizerMiddleware.create({
  runtimeVersion: true
});

Best Practice: Cache server-side-rendered AMPs

To achieve best performance, those transformations shouldn't be applied for every request. Instead, transformations should only be applied the first time a page is requested, and the results then cached. Caching can happen on the CDN level, on the site's internal infrastructure (e.g.: Memcached), or even on the server itself, if the set of pages is small enough to fit in memory.

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