nextscript

v0.0.5

Published

3 years ago

A custom Next script loader for Next.js. Replaces the built-in NextScript component and allows you to apply polyfill pre-loading and business logic.

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eacoder

barrysteyn

barry-engineerapart

next.js nextjs next nextscript polyfills preload preloader

NextScript 💠

This project is not-so-cleverly named after the export of the same name in the amazing Next.js framework.

This component provides a flexible, business-rule oriented approach to loading the scripts in your Next project. By default, Next loads all scripts on page load, which may or may not be desirable behavior. Some of the reasons you may want to avoid that are:

Performance: Only load these scripts when needed, or wait until the page load event (for things like _error, if you know it is not needed immediately)
Preloading: It is not uncommon to need to run a script - or load a script from URL - before allowing your Next app to load.
Polyfill preloading: This is the most common application of the previous point. Next bundles some polyfills, but only the ones NEXT requires - not the ones YOU require. If you require IntersectionObserver for example, it is on you to load it yourself. Since that is a HUGE polyfill (7kb minzipped!), you do not want to deliver it to all clients - only the ones that absolutely require it (IE <= 11, Safari ALL).

This NextScript component allows you to accomplish these goals and more in a flexible, minimal way. This component itself compiles down to 2.3kb minzipped (although it is only ever executed on the server!) and has a simple API.

Built originally out of the NextScript component itself, all of that functionality is supported, in addition to the features above.

Opt-In

This component's functionality is opt-in. You can configure the component to behave exactly as NextScript itself does, or you can optionally enable the above features. Simply rendering <NextScript /> will produce identical behavior to the component found in Next.

Getting started

Install from npm:

npm i @engineerapart/nextscript

# or

yarn add @engineerapart/nextscript

You will find an entry in NPM under nextscript. This is our placeholder to avoid confusion with potential package collisions and is not the published package.

Examples

Duplicate Next.js

The only difference between this example and the default Next _document is where NextScript is imported from:

import { NextScript } from '@engineerapart/nextscript';
import Document, { Head, Main } from 'next/document';

export default class MyDocument extends Document {
  static async getInitialProps(ctx) {
    const initialProps = await Document.getInitialProps(ctx);
    return { ...initialProps };
  }

  render() {
    return (
      <html>
        <Head>
          <style>{`body { margin: 0 } /* custom! */`}</style>
        </Head>
        <body className="custom_class">
          <Main />
          <NextScript />
        </body>
      </html>
    );
  }
}

Preload polyfills

The canonical example: How to preload polyfills, including polyfills not defined by this project.

import { NextScript, FeaturePolyfills } from '@engineerapart/nextscript';
import Document, { Head, Main } from 'next/document';

const features = [
  FeaturePolyfills.FETCH,
  FeaturePolyfills.CustomEvent,
  {
    test: `('entries' in Array.prototype)`,
    feature: 'Array.prototype.entries',
  },
];

export default class MyDocument extends Document {
  static async getInitialProps(ctx) {
    const initialProps = await Document.getInitialProps(ctx);
    return { ...initialProps };
  }

  render() {
    return (
      <html>
        <Head></Head>
        <body className="custom_class">
          <Main />
          <NextScript features={features} />
        </body>
      </html>
    );
  }
}

Polyfill Service

Current this component points to the Polyfill.io service, which serves ~150 million polyfill requests per DAY (4.5 billion/month!). However, eventually this project will also support pointing to your own self-hosted polyfill service, provided that it adheres to the Polyfill.io API (instructions for self-hosting the Polyfill.io service can be found in their repository.)

How it works

The default NextScript implementation captures the scripts generated by the Next build process and immediately renders them to <script> tags in its render() function.

This component takes a different approach: It collects the same script information from the build that the original Next component does, but instead of immediately rendering them, it inserts the script information into a preloader script. The provides the opportunity to:

Load something else first
Load something else after
Load them on command

After you've configured the component, it will execute your configurations inside the preloader, and then execute the Next scripts. If you don't configure the component, it does exactly the same thing that the original Next component does!

API

You can configure the component to behave exactly as NextScript itself does, or you can optionally enable the above features. Simply rendering <NextScript /> will produce identical behavior to the component found in Next.

`NextScript` Properties

If you are using Typescript, TS will automatically detect the typings, included with this project, and provide intellisense if you are using a TS-aware editor. These properties are also documented here.

All properties are optional. Rendering this component as <NextScript /> simply duplicates exactly what the NextScript component included with Next does.

`ScriptEntry` Interface

Defined in Typescript, this interface consists of the following fields:

If you need to load arbitrary scripts, you can mount a script node before this element in your Next project. It's on our list to support, so it is coming!

`PolyfillDefinition` Interface

This project supplies a small collection of default polyfill definitions to get you started, but does not currently support all 194 polyfills supported by Polyfill.io! Thus, it was important to be able to allow you to define arbitrary polyfills. This is accomplished by providing the following object to the features prop of NextScript.

Defined in Typescript, this interface consists of the following fields:

TODO

Support a self-hosted Polyfill service
Add all known polyfills to the FeaturePolyfills collection
Support inline scripts to be injected in the preloader

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