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Server Rendering ​

This package implements generic support for server-side rendering in Meteor apps, by providing a mechanism for injecting fragments of HTML into the <head> and/or <body> of the application's initial HTML response.

Usage ​

This package exports a function named onPageLoad which takes a callback function that will be called at page load (on the client) or whenever a new request happens (on the server).

The callback receives a sink object, which is an instance of either ClientSink or ServerSink depending on the environment. Both types of sink have the same methods, though the server version accepts only HTML strings as content, whereas the client version also accepts DOM nodes.

The current interface of {Client,Server}Sink objects is as follows:

js
class Sink {
  // Appends content to the <head>.
  appendToHead(content)

  // Appends content to the <body>.
  appendToBody(content)

  // Appends content to the identified element.
  appendToElementById(id, content)

  // Replaces the content of the identified element.
  renderIntoElementById(id, content)

  // Redirects request to new location.
  redirect(location, code)


  // server only methods

  // sets the status code of the response.
  setStatusCode(code)

  // sets a header of the response.
  setHeader(key, value)

  // gets request headers
  getHeaders()

  // gets request cookies
  getCookies()
}

The sink object may also expose additional properties depending on the environment. For example, on the server, sink.request provides access to the current request object, and sink.arch identifies the target architecture of the pending HTTP response (e.g. "web.browser").

Here is a basic example of onPageLoad usage on the server:

js
import from "react";
import { renderToString } from "react-dom/server";
import { onPageLoad } from "meteor/server-render";

import App from "/imports/Server.js";

onPageLoad(sink => {
  sink.renderIntoElementById("app", renderToString(
    <App location={sink.request.url} />
  ));
});

Likewise on the client:

js
import React from "react";
import ReactDOM from "react-dom";
import { onPageLoad } from "meteor/server-render";

onPageLoad(async (sink) => {
  const App = (await import("/imports/Client.js")).default;
  ReactDOM.hydrate(<App />, document.getElementById("app"));
});

Note that the onPageLoad callback function is allowed to return a Promise if it needs to do any asynchronous work, and thus may be implemented by an async function (as in the client case above).

Note also that the client example does not end up calling any methods of the sink object, because ReactDOM.hydrate has its own similar API. In fact, you are not even required to use the onPageLoad API on the client, if you have your own ideas about how the client should do its rendering.

Here is a more complicated example of onPageLoad usage on the server, involving the styled-components npm package:

js
import React from "react";
import { onPageLoad } from "meteor/server-render";
import { renderToString } from "react-dom/server";
import { ServerStyleSheet } from "styled-components";
import App from "/imports/Server";

onPageLoad((sink) => {
  const sheet = new ServerStyleSheet();
  const html = renderToString(
    sheet.collectStyles(<App location={sink.request.url} />)
  );

  sink.renderIntoElementById("app", html);
  sink.appendToHead(sheet.getStyleTags());
});

In this example, the callback not only renders the <App /> element into the element with id="app", but also appends any <style> tag(s) generated during rendering to the <head> of the response document.

Although these examples have all involved React, the onPageLoad API is designed to be generically useful for any kind of server-side rendering.

Streaming HTML ​

React 16 introduced renderToNodeStream, which enables the reading of rendered HTML in chunks. This reduces the TTFB (time to first byte).

Here is a renderToNodeStream example using styled-components. Note the use of sheet.interleaveWithNodeStream instead of sink.appendToHead(sheet.getStyleTags());:

js
import React from "react";
import { onPageLoad } from "meteor/server-render";
import { renderToNodeStream } from "react-dom/server";
import { ServerStyleSheet } from "styled-components";
import App from "/imports/Server";

onPageLoad((sink) => {
  const sheet = new ServerStyleSheet();
  const appJSX = sheet.collectStyles(<App location={sink.request.url} />);
  const htmlStream = sheet.interleaveWithNodeStream(renderToNodeStream(appJSX));
  sink.renderIntoElementById("app", htmlStream);
});

Getting data from the request ​

In some cases you want to customize meta tags or something else in your response based in the requested URL, for example, if your are loading a page with a specific product in your app maybe you want to include an image and a description for social previews.

You can extract information from the request using the sink object.

js
import { onPageLoad } from "meteor/server-render";

const getBaseUrlFromHeaders = (headers) => {
  const protocol = headers["x-forwarded-proto"];
  const { host } = headers;
  // we need to have '//' to findOneByHost work as expected
  return `${protocol ? `${protocol}:` : ""}//${host}`;
};

const getContext = (sink) => {
  // more details about this implementation here
  // https://github.com/meteor/meteor/issues/9765
  const { headers, url, browser } = sink.request;
  // no useful data will be found for galaxybot requests
  if (browser && browser.name === "galaxybot") {
    return null;
  }

  // when we are running inside cordova we don't want to resolve meta tags
  if (url && url.pathname && url.pathname.includes("cordova/")) {
    return null;
  }

  const baseUrl = getBaseUrlFromHeaders(headers);
  const fullUrl = `${baseUrl}${url.pathname || ""}`;

  return { baseUrl, fullUrl };
};

onPageLoad((sink) => {
  const { baseUrl, fullUrl } = getContext(sink);

  // product URL contains /product on it
  const urlParseArray = fullUrl.split("/");

  const productPosition = urlParseArray.indexOf("product");
  const productId =
    productPosition !== -1 &&
    urlParseArray[productPosition + 1].replace("?", "");
  const product = productId && ProductsCollection.findOne(productId);

  const productTitle = product && `Buy now ${product.name}, ${product.price}`;
  if (productTitle) {
    sink.appendToHead(`<title>${productTitle}</title>\n`);
    sink.appendToHead(`<meta property="og:title" content="${productTitle}">\n`);
    if (product.imageUrl) {
      sink.appendToHead(
        `<meta property="og:image" content="${product.imageUrl}">\n`
      );
    }
  }
});