Peterbe.com

tl;dr; If you know that the only I/O you have is disk and the disk is SSD, then synchronous is probably more convenient, faster, and more memory lean.

I'm not a NodeJS expert so I could really do with some eyes on this.

There is little doubt in my mind that it's smart to use asynchronous ideas when your program has to wait for network I/O. Because network I/O is slow, it's better to let your program work on something else whilst waiting. But disk is actually fast. Especially if you have SSD disk.

The context

I'm working on a Node program that walks a large directory structure and looks for certain file patterns, reads those files, does some processing and then exits. It's a cli basically and it's supposed to work similar to jest where you tell it to go and process files and if everything worked, exit with 0 and if anything failed, exit with something >0. Also, it needs to be possible to run it so that it exits immediately on the first error encountered. This is similar to running jest --bail.

My program needs to process thousands of files and although there are thousands of files, they're all relatively small. So first I wrote a simple reference program: https://github.com/peterbe/megafileprocessing/blob/master/reference.js
What it does is that it walks a directory looking for certain .json files that have certain keys that it knows about. Then, just computes the size of the values and tallies that up. My real program will be very similar except it does a lot more with each .json file.

You run it like this:

▶ CHAOS_MONKEY=0.001 node reference.js ~/stumptown-content/kumadocs -q
Error: Chaos Monkey!
    at processDoc (/Users/peterbe/dev/JAVASCRIPT/megafileprocessing/reference.js:37:11)
    at /Users/peterbe/dev/JAVASCRIPT/megafileprocessing/reference.js:80:21
    at Array.forEach (<anonymous>)
    at main (/Users/peterbe/dev/JAVASCRIPT/megafileprocessing/reference.js:78:9)
    at Object.<anonymous> (/Users/peterbe/dev/JAVASCRIPT/megafileprocessing/reference.js:99:20)
    at Module._compile (internal/modules/cjs/loader.js:956:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:973:10)
    at Module.load (internal/modules/cjs/loader.js:812:32)
    at Function.Module._load (internal/modules/cjs/loader.js:724:14)
    at Function.Module.runMain (internal/modules/cjs/loader.js:1025:10)
Total length for 4057 files is 153953645
1 files failed.

(The environment variable CHAOS_MONKEY=0.001 makes it so there's a 0.1% chance it throws an error)

It processed 4,057 files and one of those failed (thanks to the "chaos monkey").
In its current state that (on my MacBook) that takes about 1 second.

It's not perfect but it's a good skeleton. Everything is synchronous. E.g.

function main(args) {
  // By default, don't exit if any error happens
  const { bail, quiet, root } = parseArgs(args);
  const files = walk(root, ".json");
  let totalTotal = 0;
  let errors = 0;
  files.forEach(file => {
    try {
      const total = processDoc(file, quiet);
      !quiet && console.log(`${file} is ${total}`);
      totalTotal += total;
    } catch (err) {
      if (bail) {
        throw err;
      } else {
        console.error(err);
        errors++;
      }
    }
  });
  console.log(`Total length for ${files.length} files is ${totalTotal}`);
  if (errors) {
    console.warn(`${errors} files failed.`);
  }
  return errors ? 1 : 0;
}

And inside the processDoc function it used const content = fs.readFileSync(fspath, "utf8");.

I/Os compared

@amejiarosario has a great blog post called "What every programmer should know about Synchronous vs. Asynchronous Code". In it, he has this great bar chart:

If you compare "SSD I/O" with "Network SFO/NCY" the difference is that SSD I/O is 456 times "faster" than SFO-to-NYC network I/O. I.e. the latency is 456 times less.

Another important aspect when processing lots of files is garbage collection. When running synchronous, it can garbage collect as soon as it has processed one file before moving on to the next. If it was asynchronous, as soon as it yields to move on to the next file, it might hold on to memory from the first file. Why does this matter? Because if the memory-usage when processing many files asynchronously bloat so hard that it actually crashes with an out-of-memory error. So what matters is avoiding that. It's OK if the program can use lots of memory if it needs to, but it's really bad if it crashes.

One way to measure this is to use /usr/bin/time -l (at least that's what it's called on macOS). For example:

▶ /usr/bin/time -l node reference.js ~/stumptown-content/kumadocs -q
Total length for 4057 files is 153970749
        0.75 real         0.58 user         0.23 sys
  57221120  maximum resident set size
         0  average shared memory size
         0  average unshared data size
         0  average unshared stack size
     64160  page reclaims
         0  page faults
         0  swaps
         0  block input operations
         0  block output operations
         0  messages sent
         0  messages received
         0  signals received
         0  voluntary context switches
      1074  involuntary context switches

Its maximum memory usage total was 57221120 bytes (55MB) in this example.

Introduce asynchronous file reading

Let's change the reference implementation to use const content = await fsPromises.readFile(fspath, "utf8");. We're still using files.forEach(file => { but within the loop the whole function is prefixed with async function main() { now. Like this:

async function main(args) {
  // By default, don't exit if any error happens
  const { bail, quiet, root } = parseArgs(args);
  const files = walk(root, ".json");
  let totalTotal = 0;
  let errors = 0;

  let total;
  for (let file of files) {
    try {
      total = await processDoc(file, quiet);
      !quiet && console.log(`${file} is ${total}`);
      totalTotal += total;
    } catch (err) {
      if (bail) {
        throw err;
      } else {
        console.error(err);
        errors++;
      }
    }
  }
  console.log(`Total length for ${files.length} files is ${totalTotal}`);
  if (errors) {
    console.warn(`${errors} files failed.`);
  }
  return errors ? 1 : 0;
}

Let's see how it works:

▶ /usr/bin/time -l node async1.js ~/stumptown-content/kumadocs -q
Total length for 4057 files is 153970749
        1.31 real         1.01 user         0.49 sys
  68898816  maximum resident set size
         0  average shared memory size
         0  average unshared data size
         0  average unshared stack size
     68107  page reclaims
         0  page faults
         0  swaps
         0  block input operations
         0  block output operations
         0  messages sent
         0  messages received
         0  signals received
         0  voluntary context switches
     62562  involuntary context switches

That means it maxed out at 68898816 bytes (65MB).

You can already see a difference. 0.79 seconds and 55MB for synchronous and 1.31 seconds and 65MB for asynchronous.

But to really measure this, I wrote a simple Python program that runs this repeatedly and reports a min/median on time and max on memory:

▶ python3 wrap_time.py /usr/bin/time -l node reference.js ~/stumptown-content/kumadocs -q
...
TIMES
BEST:   0.74s
WORST:  0.84s
MEAN:   0.78s
MEDIAN: 0.78s
MAX MEMORY
BEST:   53.5MB
WORST:  55.3MB
MEAN:   54.6MB
MEDIAN: 54.8MB

And for the asynchronous version:

▶ python3 wrap_time.py /usr/bin/time -l node async1.js ~/stumptown-content/kumadocs -q
...
TIMES
BEST:   1.28s
WORST:  1.82s
MEAN:   1.39s
MEDIAN: 1.31s
MAX MEMORY
BEST:   65.4MB
WORST:  67.7MB
MEAN:   66.7MB
MEDIAN: 66.9MB

Promise.all version

I don't know if the async1.js is realistic. More realistically you'll want to not wait for one file to be processed (asynchronously) but start them all at the same time. So I made a variation of the asynchronous version that looks like this instead:

async function main(args) {
  // By default, don't exit if any error happens
  const { bail, quiet, root } = parseArgs(args);
  const files = walk(root, ".json");
  let totalTotal = 0;
  let errors = 0;

  let values;
  values = await Promise.all(
    files.map(async file => {
      try {
        total = await processDoc(file, quiet);
        !quiet && console.log(`${file} is ${total}`);
        return total;
      } catch (err) {
        if (bail) {
          console.error(err);
          process.exit(1);
        } else {
          console.error(err);
          errors++;
        }
      }
    })
  );
  totalTotal = values.filter(n => n).reduce((a, b) => a + b);
  console.log(`Total length for ${files.length} files is ${totalTotal}`);
  if (errors) {
    console.warn(`${errors} files failed.`);
    throw new Error("More than 0 errors");
  }
}

You can see the whole file here: async2.js

The key difference is that it uses await Promise.all(files.map(...)) instead of for (let file of files) {.
Also, to accomplish the ability to bail on the first possible error it needs to use process.exit(1); within the callbacks. Not sure if that's right but from the outside, you get the desired effect as a cli program. Let's measure it too:

▶ python3 wrap_time.py /usr/bin/time -l node async2.js ~/stumptown-content/kumadocs -q
...
TIMES
BEST:   1.44s
WORST:  1.61s
MEAN:   1.52s
MEDIAN: 1.52s
MAX MEMORY
BEST:   434.0MB
WORST:  460.2MB
MEAN:   453.4MB
MEDIAN: 456.4MB

Note how this uses almost 10x max. memory. That's dangerous if the processing is really memory hungry individually.

When asynchronous is right

In all of this, I'm assuming that the individual files are small. (Roughly, each file in my experiment is about 50KB)
What if the files it needs to read from disk are large?

As a simple experiment read /users/peterbe/Downloads/Keybase.dmg 20 times and just report its size:

for (let x = 0; x < 20; x++) {
  fs.readFile("/users/peterbe/Downloads/Keybase.dmg", (err, data) => {
    if (err) throw err;
    console.log(`File size#${x}: ${Math.round(data.length / 1e6)} MB`);
  });
}

See the simple-async.js here. Basically it's this:

for (let x = 0; x < 20; x++) {
  fs.readFile("/users/peterbe/Downloads/Keybase.dmg", (err, data) => {
    if (err) throw err;
    console.log(`File size#${x}: ${Math.round(data.length / 1e6)} MB`);
  });
}

Results are:

▶ python3 wrap_time.py /usr/bin/time -l node simple-async.js
...
TIMES
BEST:   0.84s
WORST:  4.32s
MEAN:   1.33s
MEDIAN: 0.97s
MAX MEMORY
BEST:   1851.1MB
WORST:  3079.3MB
MEAN:   2956.3MB
MEDIAN: 3079.1MB

And the equivalent synchronous simple-sync.js here.

for (let x = 0; x < 20; x++) {
  const largeFile = fs.readFileSync("/users/peterbe/Downloads/Keybase.dmg");
  console.log(`File size#${x}: ${Math.round(largeFile.length / 1e6)} MB`);
}

It performs like this:

▶ python3 wrap_time.py /usr/bin/time -l node simple-sync.js
...
TIMES
BEST:   1.97s
WORST:  2.74s
MEAN:   2.27s
MEDIAN: 2.18s
MAX MEMORY
BEST:   1089.2MB
WORST:  1089.7MB
MEAN:   1089.5MB
MEDIAN: 1089.5MB

So, almost 2x as slow but 3x as much max. memory.

Lastly, instead of an iterative loop, let's start 20 readers at the same time (simple-async2.js):

Promise.all(
  [...Array(20).fill()].map((_, x) => {
    return fs.readFile("/users/peterbe/Downloads/Keybase.dmg", (err, data) => {
      if (err) throw err;
      console.log(`File size#${x}: ${Math.round(data.length / 1e6)} MB`);
    });
  })
);

And it performs like this:

▶ python3 wrap_time.py /usr/bin/time -l node simple-async2.js
...
TIMES
BEST:   0.86s
WORST:  1.09s
MEAN:   0.96s
MEDIAN: 0.94s
MAX MEMORY
BEST:   3079.0MB
WORST:  3079.4MB
MEAN:   3079.2MB
MEDIAN: 3079.2MB

So quite naturally, the same total time as the simple async version but uses 3x max. memory every time.

Ergonomics

I'm starting to get pretty comfortable with using promises and async/await. But I definitely feel more comfortable without. Synchronous programs read better from an ergonomics point of view. The async/await stuff is just Promises under the hood and it's definitely an improvement but the synchronous versions just have a simpler "feeling" to it.

Conclusion

I don't think it's a surprise that the overhead of event switching adds more time than its worth when the individual waits aren't too painful.

A major flaw with synchronous programs is that they rely on the assumption that there's no really slow I/O. So what if the program grows and morphs so that it someday does depend on network I/O then your synchronous program is "screwed" since an asynchronous version would run circles around it.

The general conclusion is; if you know that the only I/O you have is disk and the disk is SSD, then synchronous is probably more convenient, faster, and more memory lean.

It started with this:

function walk(directory, filepaths = []) {
    const files = fs.readdirSync(directory);
    for (let filename of files) {
        const filepath = path.join(directory, filename);
        if (fs.statSync(filepath).isDirectory()) {
            walk(filepath, filepaths);
        } else if (path.extname(filename) === '.md') {
            filepaths.push(filepath);
        }
    }
    return filepaths;
}

And you use it like this:

const foundFiles = walk(someDirectoryOfMine);
console.log(foundFiles.length);

I thought, perhaps it's faster or better to use glob. So I installed that.
Then I found, fast-glob which sounds faster. You use both in a synchronous way.

I have a directory with about 450 files, of which 320 of them are .md files. Let's compare:

walk: 10.212ms
glob: 37.492ms
fg: 14.200ms

I measured it using console.time like this:

console.time('walk');
const foundFiles = walk(someDirectoryOfMine);
console.timeEnd('walk');
console.log(foundFiles.length);

I suppose those packages have other fancier features but, I guess this just goes to show, keep it simple.

UPDATE June 2021

The origins of this blog post were that I need a simple function to find files on disk. Later, the requirements became a bit more complex so I needed something a bit more advanced. In shopping around I found fdir which, from testing, performed excellently and has a great API (and documentation). I would handsdown use that again.

I'm working on a CLI in Node. What the CLI does it that it takes one set of .json files, compute some stuff, and spits out a different set of .json files. But what it does is not important. I wanted the CLI to feel flexible and powerful but also quite forgiving. And if you typo something, it should bubble up an error rather than redirecting it to something like console.error("not a valid file!").

Basically, you use it like this:

node index.js /some/directory
# or
node index.js /some/directory /some/other/directory
# or 
node index.js /some/directory/specificfile.json
# or
node index.js /some/directory/specificfile.json /some/directory/otherfile.json
# or
node index.js "/some/directory/*.json"
# or 
node index.js "/some/directory/**/*.json"

(Note that when typing patterns in the shell you have quote them, otherwise the shell will do the expansion for you)

Or, any combination of all of these:

node index.js "/some/directory/**/*.json" /other/directory /some/specific/file.json 

Whatever you use, with patterns, in particular, it has to make the final list of found files distinct and ordered by the order of the initial arguments.

Here's what I came up with:

import fs from "fs";
import path from "path";
// https://www.npmjs.com/package/glob
import glob from "glob";


/** Given an array of "things" return all distinct .json files.
 *
 * Note that these "things" can be a directory, a file path, or a
 * pattern.
 * Only if each thing is a directory do we search for *.json files
 * in there recursively.
 */
function expandFiles(directoriesPatternsOrFiles) {
  function findFiles(directory) {
    const found = glob.sync(path.join(directory, "*.json"));

    fs.readdirSync(directory, { withFileTypes: true })
      .filter(dirent => dirent.isDirectory())
      .map(dirent => path.join(directory, dirent.name))
      .map(findFiles)
      .forEach(files => found.push(...files));

    return found;
  }

  const filePaths = [];
  directoriesPatternsOrFiles.forEach(thing => {
    let files = [];
    if (thing.includes("*")) {
      // It's a pattern!
      files = glob.sync(thing);
    } else {
      const lstat = fs.lstatSync(thing);
      if (lstat.isDirectory()) {
        files = findFiles(thing);
      } else if (lstat.isFile()) {
        files = [thing];
      } else {
        throw new Error(`${thing} is neither file nor directory`);
      }
    }
    files.forEach(p => filePaths.includes(p) || filePaths.push(p));
  });
  return filePaths;
}

This is where I'm bracing myself for comments that either point out something obvious that Node experts know or some awesome npm package that already does this but better.

If you have a typo, you get an error thrown that looks something like this:

Error: ENOENT: no such file or directory, lstat 'mydirectorrry'

(assuming mydirectory exists but mydirectorrry is a typo)

tl;dr; The previous (React) total JavaScript bundle size was: 36.2K Brotli compressed. The new (Preact) JavaScript bundle size was: 5.9K. I.e. 6 times smaller. Also, it appears to load faster in WebPageTest.

I have this page that is a Django server-side rendered page that has on it a form that looks something like this:

<div id="root">  
  <form action="https://songsear.ch/q/">  
    <input type="search" name="term" placeholder="Type your search here..." />
    <button>Search</button>
  </form>  
</div>

It's a simple search form. But, to make it a bit better for users, I wrote a React widget that renders, into this document.querySelector('#root'), a near-identical <form> but with autocomplete functionality that displays suggestions as you type.

Anyway, I built that React bundle using create-react-app. I use the yarn run build command that generates...

• css/main.83463791.chunk.css - 1.4K
• js/main.ec6364ab.chunk.js - 9.0K (gzip 2.8K, br 2.5K)
• js/runtime~main.a8a9905a.js - 1.5K (gzip 754B, br 688B)
• js/2.b944397d.chunk.js - 119K (gzip 36K, br 33K)

Then, in Python, a piece of post-processing code copies the files from the build/static/ directory and inserts it into the rendered HTML file. The CSS gets injected as an inline <style> tag.

It's a simple little widget. No need for any service-workers or react-router or any global state stuff. (Actually, it only has 1 single runtime dependency outside the framework) I thought, how about moving this to Preact?

In comes preact-cli

The app used a couple of React hooks but they were easy to transform into class components. Now I just needed to run:

npx preact create --yarn widget name-of-my-preact-project
cd name-of-my-preact-project
mkdir src
cp ../name-of-React-project/src/App.js src/
code src/App.js

Then, I slowly moved over the src/App.js from the create-react-app project and slowly by slowly I did the various little things that you need to do. For example, to learn to build with preact build --no-prerender --no-service-worker and how I can override the default template.

Long story short, the new built bundles look like this:

• style.82edf.css - 1.4K
• bundle.d91f9.js - 18K (gzip 6.4K, br 5.9K)
• polyfills.9168d.js - 4.5K (gzip 1.8K, br 1.6K)

(The polyfills.9168d.js gets injected as a script tag if window.fetch is falsy)

Unfortunately, when I did the move from React to Preact I did make some small fixes. Doing the "migration" I noticed a block of code that was never used so that gives the build bundle from Preact a slight advantage. But I think it's nominal.

In conclusion: The previous total JavaScript bundle size was: 36.2K (Brotli compressed). The new JavaScript bundle size was: 5.9K (Brotli compressed). I.e. 6 times smaller. But if you worry about the total amount of JavaScript to parse and execute, the size difference uncompressed was 129K vs. 18K. I.e. 7 times smaller. I can only speculate but I do suspect you need less CPU/battery to process 18K instead of 129K if CPU/batter matters more (or closer to) than network I/O.

Rendering speed difference

Rendering speed is so darn hard to measure on the web because the app is so small. Plus, there's so much else going on that matters.

However, using WebPageTest I can do a visual comparison with the "Mobile - Slow 3G" preset. It'll be a somewhat decent measurement of the total time of downloading, parsing and executing. Thing is, the server-side rended HTML form has a button. But the React/Preact widget that takes over the DOM hides that submit button. So, using the screenshots that WebPageTest provides, I can deduce that the Preact widget completes 0.8 seconds faster than the React widget. (I.e. instead of 4.4s it became 3.9s)

Truth be told, I'm not sure how predictable or reproducible is. I ran that WebPageTest visual comparison more than once and the results can vary significantly. I'm not even sure which run I'm referring to here (in the screenshot) but the React widget version was never faster.

Conclusion and thoughts

Unsurprisingly, Preact is smaller because you simply get less from that framework. E.g. synthetic events. I was lucky. My app uses onChange which I could easily "migrate" to onInput and I managed to get it to work pretty easily. I'm glad the widget app was so small and that I don't depend on any React specific third-party dependencies.

But! In WebPageTest Visual Comparison it was on "Mobile - Slow 3G" which only represents a small portion of the traffic. Mobile is a huge portion of the traffic but "Slow 3G" is not. When you do a Desktop comparison the difference is roughtly 0.1s.

Also, in total, that page is made up of 3 major elements

1. The server-side rendered HTML
2. The progressive JavaScript widget (what this blog post is about)
3. A piece of JavaScript initiated banner ad

That HTML controls the "First Meaningful Paint" which takes 3 seconds. And the whole shebang, including the banner ad, takes a total of about 9s. So, all this work of rewriting a React app to Preact saved me 0.8s out of the total of 9s.

Web performance is hard and complicated. Every little counts, but keep your eye on the big ticket items assuming there's something you can do about them.

At the time of writing, preact-cli uses Preact 8.2 and I'm eager to see how Preact X feels. Apparently, since April 2019, it's in beta. Looking forward to giving it a try!

I use localhost:3000 for a lot of different projects. It's the default port on create-react-app's dev server. The browser profile remains but projects come and go. There's a lot of old stuff in there that I have no longer any memory of adding.

Working in a recent single page app, I tried to use localStorage as a cache for some XHR requests and got: DOMException: "The quota has been exceeded.".
Wat?! I'm only trying to store a ~250KB JSON string. Surely that's far away from the mythical 5MB limit. Do I really have to lzw compress the string in and out to save room and pay for it in CPU cycles?

Better yet, find out what junk I still have in there.

Paste this into your Web Console (it's safe as milk):

Object.entries(localStorage).forEach(([k,v]) => console.log(k.padEnd(50), v.length, (v.length / 1024).toFixed(1) + 'KB'))

The output looks something like this:

Or, sorted and filtered a bit:

Object.entries(localStorage).sort((a, b) => b[1].length -a[1].length).slice(0,5).forEach(
([k,v]) => console.log(k.padEnd(50), v.length, (v.length / 1024).toFixed(1) + 'KB'));

Looks like this:

And for the record, summed total in kilobytes:

(Object.values(localStorage).map(x => x.length).reduce((a, b) => a + b) / 1024).toFixed(1) + 'KB';

Wrapping up

Seems my Firefox browser's localStorage limit is still 5MB.

Also, you can do the loop using localStorage.length and localStorage.key(n) and localStorage.getItem(localStorage.key(n)).length but using Object.entries(localStorage) seems neater.

I guess this means I can still use localStorage in my app. It seems I just need to localStorage.removeItem('massive-list:items') which sounds like an experiment, from eons ago, for seeing how much I can stuff in there.

tl;dr; The main JavaScript bundle goes from 29KB to 6KB by switching from JQuery to Cash. Both with Brotli compression.

In Web Performance, every byte counts. Downloading less stuff means faster network operations but for JavaScript it also means less to parse and execute. This site used use JQuery 3.4.1 but now uses Cash 4.1.2. It requires some changes to how you use $ and most noticeable is the lack of animations and $.ajax.

I still stand by the $ function. It's great when you have a regular (static) website that isn't a single page app but still needs a little bit of interactive JavaScript functionality. On this site, I use it for making the commenting work and some various navigation/header stuff.

Switching to Cash means you have to stop doing things like $.getJSON() and $('.classname').fadeIn(400) which, in a sense, gives Cash an unfair advantage because those bits take up a large portion of the bundle size. Yes, there is a custom build of jQuery without those but check out this size comparison:

Bundle	Uncompressed (bytes)	Gzipped (bytes)
jQuery 3.4.1	88,145	30,739
jQuery 3.4.1 Slim	71,037	24,403
Cash 4.1.2	14,818	5,167

I still needed a fadeIn function, which I was relying on from jQuery, but to remedy that I just copied one of these from youmightnotneedjquery.com. It would be better to not do that an use a CSS transform instead but, well, I'm only human.

Before: with jQuery

Another thing you'll need to replace is to switch from $.ajax to fetch but there are good polyfills but I haven't bothered with polyfills because the tiny percentage of visitors I have, without fetch support still get a working site but can't post comments.

I was contemplating doing what GitHub did in 2018 which was to replace jQuery with real vanilla JavaScript code but it didn't seem worth it now that Cash is only 5KB (gzipped) and it's an actively maintained project too.

Before: with jQuery

After: with Cash

Back in 2012, I did an experiment to compare if and/or how much faster WebSockets are compared to AJAX (aka. XHR). It would be a "protocol benchmark" to see which way was faster to schlep data back and forth between a server and a browser in total. The conclusion of that experiment was that WebSockets were faster but when you take latency into account, the difference was minimal. Considering the added "complexities" of WebSockets (keeping connections, results don't come where the request was made, etc.) it's not worth it.

But, 7 years later browsers are very different. Almost all browsers that support JavaScript also support WebSockets. HTTP/2 might make things better too. And perhaps the WebSocket protocol is just better implemented in the browsers. Who knows? An experiment knows.

So I made a new experiment with similar tech. The gist of the code is best explained with some code:

// Inside App.js

loopXHR = async count => {
  const res = await fetch(`/xhr?count=${count}`);
  const data = await res.json();
  const nextCount = data.count;
  if (nextCount) {
    this.loopXHR(nextCount);
  } else {
    this.endXHR();
  }
};

Basically, pick a big number (e.g. 100) and send that integer to the server which does this:

# Inside app.py 

# from the the GET querystring "?count=123"
count = self.get_argument("count")   
data = {"count": int(count) - 1}
self.write(json.dumps(data))

So the browser keeps sending the number back to the server that decrements it and when the server returns 0 the loop ends and you look how long the whole thing took.

Try It

The code is here: https://github.com/peterbe/sockshootout2019

And the demo app is here: https://sockshootout.app (Just press "Start!", wait and press it 2 or 3 more times)

Location, location, location

What matters is the geographical distance between you and the server. The server used in this experiment is in New York, USA.

What you'll find is that the closer you are to the server (lower latency) the better WebSocket performs. Here's what mine looks like:

My result between South Carolina, USA and New York, USA

Now, when I run the whole experiment all on my laptop the results look very different:

Running all locally

I don't have a screenshot for it but a friend of mine ran this from his location in Perth, Australia. There was no difference. If any difference it was "noise".

Same Conclusion?

Yes, latency matters most. The technique, for the benefit of performance, doesn't matter much.

No matter how fancy you're trying to be, what matters is the path the bytes have to travel. Or rather, the distance the bytes have to travel. If you're far away a large majority of the total time is sending and receiving the data. Not the time it takes the browser (or the server) to process it.

However, suppose you do have all your potential clients physically near the server, it might be beneficial to use WebSockets.

Thoughts and Conclusions

My original thought was to use WebSockets instead of XHR for an autocomplete widget. At almost every keystroke, you send it to the server and as search results come in, you update the search result display. Things like that need to be fast and "snappy". But that's not where WebSockets shine. They shine in their ability to actively await results without having a loop that periodically pulls. There's nothing wrong with WebSocket and it has its brilliant use cases.

In summary, don't bother just to get a single-digit percentage performance increase if the complexity of the code and infrastructure is non-trivial. Keep building cool stuff with WebSockets but if you expect one result per action, XHR is good enough.

Bonus

The experiment app does collect everyone's results (just the timings and IP) and I hope to find the time to process this and build graph a correlating the geographical distance compared to the difference between the two techniques. Watch this space!

By the way, if you do plan on writing some WebSocket implementation code I highly recommend Sockette. It's solid and easy to use.

A couple of months ago my colleague Michael @mythmon Cooper wanted to add a feature to the front-end code of Whatsdeployed and learned that the whole front-end is spaghetti jQuery code. So, instead, he re-wrote it in React. My only requirements were "Use create-react-app and no redux", i.e. keep it simple.

We also took the opportunity to rewrite some of the ways that URLs are handled. It used to be that a "short link" would redirect. For example GET /s-5HY would return 302 to Location: ?org=mozilla&repo=tecken&name[]=Dev&url[]=https://symbols.dev.mozaws.net/__version__&name[]=Stage... Basically, the short link was just an alias for a redirect. Just like those services like bit.ly or g.co. Now, the short link is a permanent fixture. The short link is included in the XHR calls to the server for getting the relevant data.

All old URLs will continue to work but now the canonical URL becomes /s/5HY/mozilla-services/tecken, for example. The :org/:repo isn't really necessary because the server knows exactly what 5HY (in this example means), but it's nice for the URL bar's memory.

Another thing that changed was how it can recognize "bors commits". When you use bors, you put a bunch of commits into a GitHub Pull Request and then ask the bors bot to merge them into master. Using "bors mode" in Whatsdeployed is optional but we believe it looks a lot more user-friendly. Here is an example of mozilla/normandy with and without bors toggled on and off.

Without "bors mode"

With "bors mode"

Thank you mythmon!

Lastly, hopefully this will make it a lot easier to contribute. Check out https://github.com/peterbe/whatsdeployed. All you need is Python 3, a PostgreSQL, and almost any version of Node that can run create-react-apps. Ping me if you find it hard to get up and running.

In a highly unscientific survey of exactly 2 French native friends, I asked them what they think about formatting large numbers the "French way" versus doing it the "English way". In particular, if the rest of content/app is English, would it be jarring if the formatting of numbers was French. Both Adrian and Mathieu said they prefer displaying the number the French way even if the app/content is French.

If you have an English browser opening https://codepen.io/peterbe/pen/xBRGoN means it's going to display the two numbers the same way. But if you have a French locale in your browser it'll look like this:

Number.toLocaleString() is now universally supported so that's no longer a worry.

For years I was using a function like this:

/* http://stackoverflow.com/a/2901298 */
function numberWithCommas(x) {
  var parts = x.toString().split('.');
  parts[0] = parts[0].replace(/\B(?=(\d{3})+(?!\d))/g, ',');
  return parts.join('.');
}

numberWithCommas(100000000);
// "100,000,000"

and it works and is reasonably fast too but it's so tempting to not use and instead stand on the shoulder-of-browsers to supply this functionality instead. But consider the alternative:

(100000000).toLocaleString();
// "100,000,000"

The thing that's always worried me is; What will someone's reaction be if the texts are in one locale and the formatting of numbers (and dates, etc!) are in another locale?

All 2 of the people I asked say they don't mind the mixing but admit that it's weird but that ultimately they prefer "their" format.

If you're non-English browser, what do you prefer? If you're a web usability expert, please, too, drop a comment to share what you think.

1. Create a create-react-app first:

create-react-app myapp

2. Enter it and install node-sass and bulmaswatch

cd myapp
yarn add bulma bulmaswatch node-sass

3. Edit the src/index.js to import index.scss instead:

-import "./index.css";
+import "./index.scss";

4. "Rename" the index.css file:

git rm src/index.css 
touch src/index.scss
git add src/index.scss

5. Now edit the src/index.scss to look like this:

@import "node_modules/bulmaswatch/darkly/bulmaswatch";

This assumes your favorite theme was the darkly one. You can obviously change that later.

6. Run the app:

BROWSER=none yarn start

7. Open the browser at http://localhost:3000

That's it! However, the create-react-app default look doesn't expose any of the cool stuff that Bulma can style. So let's rewrite our src/App.js by copying the minimal starter HTML from the Bulma documentation. So make the src/App.js component look something like this:

class App extends Component {
  render() {
    return (
      <section className="section">
        <div className="container">
          <h1 className="title">Hello World</h1>
          <p className="subtitle">
            My first website with <strong>Bulma</strong>!
          </p>
        </div>
      </section>
    );
  }
}

Now it'll look like this:

Yes, it's not much but it's a great start. Over to you to take this to infinity and beyond!

Not So Secret Sauce

In the rushed instructions above the choice of theme was darkly. But what you need to do next is go to https://jenil.github.io/bulmaswatch/, click around and eventually pick the one you like. Suppose you like spacelab, then you just change that @import ... line to be:

@import "node_modules/bulmaswatch/spacelab/bulmaswatch";

TEMPORARY:

h1 {  
    color: red;
    font-size: 5em;
}

TEST CHANGE 3.