What's new in Node.js 9?

Node.js 8.9.0 just became the LTS (Long Term Support) version of Node.js under the codename Carbon, and it will be maintained till December 31, 2019, to align with the scheduled end-of-life of OpenSSL-1.0.2.

After that, Node.js 9 will serve as the base for the next LTS release, Node.js 10, which will become the active LTS version in October 2018. To read more on Node.js releases, read the official Node.js Releases repository.

HTTP/2 without the --expose-http2 flag

HTTP/2 landed in Node.js 8.4 behind a flag. With Node.js 9, it became always available. If you are new to HTTP/2, I recommend checking out the following resources:

• HTTP/2 by EITF
• Introduction to HTTP/2
• Rules of Thumb for HTTP/2 Push

You can start using HTTP/2 with the http2 core module:

const http2 = require("http2");
const fs = require("fs");

const server = http2.createSecureServer({
  key: fs.readFileSync("key.pem"),
  cert: fs.readFileSync("cert.pem"),
});

server.on("error", (err) => console.error(err));
server.on("socketError", (err) => console.error(err));

server.on("stream", (stream, headers) => {
  // stream is a Duplex
  stream.respond({
    "content-type": "text/html",
    ":status": 200,
  });
  stream.end("<h1>Hello World</h1>");
});

server.listen(8443);

To run the example above, you have to generate a private key and a certificate for your server. To do so, run this command: openssl req -newkey rsa:2048 -new -nodes -x509 -days 3650 -keyout key.pem -out cert.pem. When it asks for the common name, make sure to enter localhost. You need this, as HTTP/2 only works using TLS to improve security.

To read more on HTTP/2, check out the official Node.js HTTP/2 documentation.

Deep strict equal helper exposed in util

The assert core module had the assert.deepStrictEqual(actual, expected[, message]) method since version 1.2.0. However, as the purpose of that function is to be used in tests, it throws if the values don't match.

Since a lot of userland modules needed this functionality, the Node.js core decided to expose this function, that it was already using internally.

From now on, you can use the util.isDeepStrictEqual(value1, value2) method to compare any values.

const { isDeepStrictEqual } = require("util");

const isEq = isDeepStrictEqual(
  {
    a: "1",
  },
  {
    a: 1,
  }
);

Callbackify added to util

util.promisify was added with Node.js 8. However, because of compatibility reasons, there was a need for the opposite - a method that can convert Promises to an error-first, callback taking function.

const { callbackify } = require("util");

async function main() {
  await Promise.resolve();
}

callbackify(main)(function (err) {
  if (err) {
    return console.error(err);
  }

  console.log("finished without an error");
});

More static error codes

During the summer, static error codes started to appear in the Node.js core to solve the problem of string comparisons when errors were thrown. You might have seen a lot of error handling logic like this previously:

if (err.message === "Can't set headers after they are sent.") {
  //do something with the error
}

The problem with this approach is that even a typo fix would cause a SemVer major change. And it gets even worse when you want to fix a misleading error message. To solve the issue, the Node.js core started to assign static error codes to errors. You can check them out on the errors docs page.

The previous example can be rewritten the following way:

if (err.code === "ERR_HTTP_HEADERS_SENT") {
  //do something with the error
}

Two-Factor Authentication for npm

Node.js 9.0.0 ships with npm version 5.5.1 - which includes two-factor authentication. If you are publishing, this is a must have - even if you don't update to Node.js 9, you should update your npm version and enable two-factor authentication.

Updating to Node.js 9?

Updating to odd-numbered major releases are generally not recommended for production environments, only if you'd like to test things out, as breaking changes can be added with each release. There will be no long-term support for these releases, and development on them will be stopped immediately once an even-numbered LTS version is cut.