Render Different UI for Mobile and Desktop

There are three different methods to render different user interfaces on mobile and desktop - CSS, window.matchMedia(), and User Agent String. These techniques can be combined.

CSS

The first one involves using CSS to render the same UI with different layouts for different screen sizes.

@media screen and (max-width: 600px) {
  // Mobile
}
@media screen and (min-width: 601px) and (max-width: 940px) {
  // Tablet
}
@media screen and (min-width: 941px) {
  // Desktop
}

Match Media API

window.matchMedia() is a browser API that can be listened to and used to check whether the a CSS media query is true or false.

function addMQListener(mq, callback) {
  if (mq.addEventListener) {
    mq.addEventListener("change", callback);
  } else {
    mq.addListener(callback);
  }
}

addMQListener(window.matchMedia("(orientation:landscape)"),
  event => {
    if (event.matches) {
      /* now in landscape orientation */
    } else {
      /* now in portrait orientation */
    }
  }
);

User Agent String

The final option is useful if SSR is important. The browser will send the user-agent header on requests to the server. This gives the server information about the device that is making the request. You can then use a regular expression to determine whether the request is coming from a mobile device or a desktop device.

Here is an example with Sveltekit pages and endpoints:

// src/routes/page.ts
export const get: RequestHandler = async ({ event }) => {
  const mobileRegex = /Mobile|iP(hone|od|ad)|Android|BlackBerry/;
  const isMobile = mobileRegex.test(event.request.headers.get("user-agent") || "");

  return {
    status: 200,
    body: {
      isMobile // pass this boolean to Svelte page
    },
  }
};

<!-- src/routes/page.svelte -->
<script lang="ts">
export let isMobile: boolean;
</script>

{#if isMobile}
  <!-- MobileComponent -->
{:else}
  <!-- DesktopComponent -->
{/else}