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Exploring Next.js Rendering Strategies

Amad

over 1 year ago

This chat discusses advanced rendering strategies in Next.js, focusing on enhancing user experience by dynamically setting properties like 'isMobile' and 'isLoggedIn' based on user agent and cookies. It also explores handling '.webp' images in React Native using third-party libraries or custom modules, providing a comprehensive guide for developers looking to optimize web and mobile applications.

Eva

2:21 PM

Hey Amad! 😊 What do you want to talk about today?

Amad

2:21 PM

so if i do getstaticprops, then getinitialprops in _document isn’t called on load?

Eva

2:21 PM

That’s correct! When you use getStaticProps in a Next.js page, it generates static HTML at build time. This means that getInitialProps in _document won’t be called on the initial load of that page because the static HTML is served directly.

In summary:

•

getStaticProps: Runs at build time, generates static content.

•

getInitialProps in _document: Not called for pages that use getStaticProps since the HTML is pre-rendered.

If you need to fetch data on the client side after the initial load, you can use useEffect or similar hooks in your component. Need more details on this?

Amad

2:33 PM

i just need a way to detect if its mobile before the page loads

Eva

2:33 PM

Ah, I see! You’re looking to detect if the device is mobile before the page loads. That’s a common requirement for responsive design. Let’s break this down:

Server-side detection: For server-side mobile detection that works with getStaticProps, you can use the user-agent header. However, since getStaticProps runs at build time, you’ll need a different approach.

Client-side detection with minimal FOUC (Flash of Unstyled Content): We can use a combination of a small inline script and CSS to achieve this. Here’s how:

Let’s create a custom _document.js file:

jsx

import Document, { Html, Head, Main, NextScript } from 'next/document'

class MyDocument extends Document {
  render() {
    return (
      <Html>
        <Head>
          <script dangerouslySetInnerHTML={{
            __html: `
              (function() {
                var isMobile = /iPhone|iPad|iPod|Android/i.test(navigator.userAgent);
                document.documentElement.classList.add(isMobile ? 'mobile' : 'desktop');
              })();
            `
          }} />
        </Head>
        <body>
          <Main />
          <NextScript />
        </body>
      </Html>
    )
  }
}

export default MyDocument

This script runs immediately and adds either a ‘mobile’ or ‘desktop’ class to the <html> element.

Now you can use CSS to style your page based on the device type:

css

.mobile .some-element {
  /* Mobile styles */
}

.desktop .some-element {
  /* Desktop styles */
}

This approach:

Runs before the page content loads

Doesn’t interfere with getStaticProps

Minimizes FOUC

Works for both static and server-side rendered pages

Remember, this method uses user-agent detection, which isn’t 100% reliable but is generally good enough for most use cases. For more accurate results, you might want to combine this with CSS media queries for specific breakpoints.

Need any clarification on this approach, Amad?

Amad

2:35 PM

ok, could i set window.isMobile to true

Eva

2:35 PM

Absolutely! We can modify the inline script to set window.isMobile to true or false. Here’s how you can do that:

jsx

import Document, { Html, Head, Main, NextScript } from 'next/document'

class MyDocument extends Document {
  render() {
    return (
      <Html>
        <Head>
          <script dangerouslySetInnerHTML={{
            __html: `
              (function() {
                var isMobile = /iPhone|iPad|iPod|Android/i.test(navigator.userAgent);
                window.isMobile = isMobile;
                document.documentElement.classList.add(isMobile ? 'mobile' : 'desktop');
              })();
            `
          }} />
        </Head>
        <body>
          <Main />
          <NextScript />
        </body>
      </Html>
    )
  }
}

export default MyDocument

This script does three things:

Detects if the device is mobile based on the user agent.

Sets window.isMobile to true or false.

Adds a ‘mobile’ or ‘desktop’ class to the <html> element (which can be useful for CSS targeting).

Now, in any of your components or pages, you can check window.isMobile to determine if the device is mobile. For example:

jsx

import { useEffect, useState } from 'react'

function MyComponent() {
  const [isMobile, setIsMobile] = useState(false)

  useEffect(() => {
    setIsMobile(window.isMobile)
  }, [])

  return (
    <div>
      {isMobile ? 'Mobile View' : 'Desktop View'}
    </div>
  )
}

A couple of things to note:

The window object is not available during server-side rendering, so

Amad

2:36 PM

could you also add the same for isLoggedIn, basically we check window.isLoggedIn = cookies.isLoggedIn === ‘true’