preload-middleware

HTTP Preload / Resource Hints / Early Hints support for Node.js server frameworks like express, koa and local-web-server.

Install

npm install --save-dev preload-middleware

Usage

Prepare a preload manifest file, e.g.

{
  "$schema": "https://raw.githubusercontent.com/http-preload/manifest/master/preload-v1.schema.json",
  "manifestVersion": 1,
  "conditions": {
    "supportsModulepreload": "(userAgentData, headers) => userAgentData.brands.some((e)=>e.brand==='Chromium'&&parseInt(e.version)>=66)"
  },
  "resources": {
    "/index.html": [
      {"rel": "preload", "href": "/assets/index.css", "as": "style"}
    ],
    "/index.html supportsModulepreload": [
      {"rel": "modulepreload", "href": "/src/foobar.js"},
      {"rel": "modulepreload", "href": "/lib/foo.js"},
      {"rel": "modulepreload", "href": "/lib/bar.js"},
      {"rel": "modulepreload", "href": "/src/qux.js"}
    ]
  }
}

For express

npm install --save-dev express

import express from 'express';
import {serveStaticPreload} from 'preload-middleware';

let app = express();
app.use('/', express.static('./public', {
  setHeaders: serveStaticPreload({
    manifestFile: './config/preload.json',
    watch: true,
  }),
}));

For koa

npm install --save-dev koa koa-static

import Koa from 'koa';
import koaStatic from 'koa-static';
import {serveStaticPreload} from 'preload-middleware';

let app = new Koa();
app.use(koaStatic('./public', {
  setHeaders: serveStaticPreload({
    manifestFile: './config/preload.json',
    watch: true,
  }),
}));

For local-web-server

Edit lws.config.js

export default {
  port: 443,
  directory: './public',
  stack: [
    'lws-request-monitor',
    'lws-compress',
    'lws-mime',
    'lws-range',
    'preload-middleware', // put preload-middleware before lws-static
    'lws-static',
    'lws-index',
  ],
  // options for preload-middleware
  preload: {
    manifestFile: './config/preload.json'
  },
};

Middleware Options

• manifestFile:string

  path to preload manifest file

• watch:boolean default false

  whether to watch the manifest file and hot reload

• index:string default "index.html"

  should be same as serve-index, or koa-static

• prefersEarlyHints:boolean default false

  if configured to be true, and user-agent supports 103 Early Hints, then links will be sent with status 103.

Examples

You can find a complete example application in preload-middleware GitHub repo.

License

Apache License 2.0