Render callbacks can now inject HTML content into multiple different
elements, and may also append content to the <head> or <body> elements, on
both the client and the server.
This new API was inspired by trying to use the styled-components npm
package on the server, which involves not only rendering and injecting
static HTML somewhere in the <body>, but also appending the resulting
<style> tag(s) into the <head>:
import { onPageLoad } from "meteor/server-render";
import { renderToString } from "react-dom/server";
import { ServerStyleSheet } from "styled-components";
onPageLoad(sink => {
const sheet = new ServerStyleSheet();
const html = renderToString(sheet.collectStyles(
<App location={sink.request.url} />
));
sink.renderIntoElementById("app", html);
sink.appendToHead(sheet.getStyleTags());
});
Note that the server-render package now exports an onPageLoad function,
rather than the old renderIntoElementById function. The functionality of
renderIntoElementById is now exposed by the {Client,Server}Sink API.
I say the client-side version of this API is 'isomorphish' to the
server-side version, because ClientSink methods can accept DOM nodes in
addition to raw HTML strings, whereas DOM nodes don't really make sense on
the server.
