use-browser

This hook enables client-side hydration of Server-Side-Rendered components where the final JS-enhanced DOM differs from the server-rendered markup. It does this by first letting the components render the server markup during hydration and — once hydrated — swap out the differing parts.

This is useful when you deliberately want to provide a different markup for clients without JavaScript with an isomorphic application, such as:

• A native <input type="select" /> on the server and a custom JavaScript-enhanced <Select /> component on the client.
• Pagination on the server which gets transformed into an infinite-scroll once client JavaScript has loaded.
• A dynamic navigation which has a static version without JavaScript.
• Other progressive-enhancements.

Installation

npm i -E @awardit/react-use-browser

If Webpack is used, ensure that the server- and client-bundles are built to node and web targets respectively (or targets which use standard module/main only on server, and browser/module/main fields on client).

For Rollup rollup-plugin-node-resolve needs to be told to load the main-field browser before module or main when it is building the browser bundle.

Usage

// app.js

import { useBrowser } from "@awardit/react-use-browser";

export const App = () => {
  const browser = useBrowser();

  if (browser) {
    return <p>This is browser markup</p>;
  }

  return <p>Server markup</p>;
};

// server.js

import { renderToString } from "react-dom/server";
import { App } from "./app";

res.write(`...
<div id="app">`, "utf-8");
res.write(renderToString(<App />), "utf-8");
res.write(`</div>
...`, "utf-8");

// client.js

import { hydrate } from "react-dom";
import { markHydrated } from "@awardit/react-use-browser";
import { App } from "./app";

const root = document.getElementById("app");

if (!root) {
  throw new Error("Missing app root");
}

hydrate(<App />, root, markHydrated);

API

useBrowser(): boolean

A hook returning true if the component is running in the browser. It will return false on the server and during client-hydration.

After client-hydration it will queue a re-render with the next render returning true.

markHydrated(): void

markHydrated should be called once hydration is finished on the client to flag that any uses of useHydrate should start with the client markup immeidiately.

If this function is not called once hydration is finished on the client then useBrowser will always perform a double-render as if it was hydrating in every new component using it, first with server-markup and then with client markup. Using markHydrated ensures that the client always renders client-markup right away from that point on.

This function will throw on the server.

FAQ

Why not use a global build variable?

Using a global variable like __BROWSER__ or process.env.BROWSER or similar will cause the resulting bundles to have differing markup making it impossible to use ReactDOM.hydrate() on the client since the markup differs.

Why not just use ReactDOM.render() on the client?

Using ReactDOM.render() to hydrate a server-rendered container is deprecated and will be removed in React 17.

Why is differing markup a problem when using ReactDOM.hydrate()?

Hydration makes assumptions about the existing markup and will not make many, if any, modifications to it when starting the application. This will shorten the time-to-interactive greatly since the application will only have to attach the required event-handlers and populate internal state.