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server-render

Documentation of Meteor's `server-render` package.
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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:

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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)
}

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:

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import React 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:

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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:

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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.

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