A blog and website by Peter Bengtsson
12 May 2020
0 comments
Node,
JavaScript
Did you know, if you can create your own new Error instance and attach your own custom properties on that? This can come in very handy when you, from the caller, want to get more structured information from the error without relying on the error message.
// WRONG ⛔️
try {
for (const i of [...Array(10000).keys()]) {
if (Math.random() > 0.999) {
throw new Error(`Failed at ${i}`);
}
}
} catch (err) {
const iteration = parseInt(err.toString().match(/Failed at (\d+)/)[1]);
console.warn(`Made it to ${iteration}`);
}
// RIGHT ✅
try {
for (const i of [...Array(10000).keys()]) {
if (Math.random() > 0.999) {
const failure = new Error(`Failed at ${i}`);
failure.iteration = i;
throw failure;
}
}
} catch (err) {
const iteration = err.iteration;
console.warn(`Made it to ${iteration}`);
}
The above examples are obviously a bit contrived but you have to imagine that whatever code can throw an error might be "far away" from where you deal with errors thrown. For example, imagine you start off a build and you want to get extra information about what the context was. In Python, you use exception classes as a form of natural filtering but JavaScript doesn't have that. Using custom error properties can be a great tool to separate unexpected errors from expected errors.
Bonus - Checking for the custom property
Imagine this refactoring:
try {
for (const i of [...Array(10000).keys()]) {
if (Math.random() > 0.999) {
const failure = new Error(`Failed at ${i}`);
failure.iteration = i;
throw failure;
}
if (Math.random() < 0.001) {
throw new Error("something else is wrong");
}
}
} catch (err) {
const iteration = err.iteration;
console.warn(`Made it to ${iteration}`);
}
With that code it's very possible you'd get Made it to undefined. So here's how you'd make the distinction:
try {
for (const i of [...Array(10000).keys()]) {
if (Math.random() > 0.999) {
const failure = new Error(`Failed at ${i}`);
failure.iteration = i;
throw failure;
}
if (Math.random() < 0.001) {
throw new Error("something else is wrong");
}
}
} catch (err) {
if (err.hasOwnProperty("iteration")) {
const iteration = err.iteration;
console.warn(`Made it to ${iteration}`);
} else {
throw err;
}
}
```
24 April 2020
0 comments
Web development,
Node,
JavaScript
minimalcss requires that you have your HTML in a serving HTTP web page so that puppeteer can open it to find out the CSS within. Suppose, in your build system, you don't yet really have a server. Well, what you can do is start one on-the-fly and shut it down as soon as you're done.
Suppose you have .html file
First install all the stuff:
yarn add minimalcss http-server
Then run it:
const path = require("path");
const minimalcss = require("minimalcss");
const httpServer = require("http-server");
const HTML_FILE = "index.html"; // THIS IS YOURS
(async () => {
const server = httpServer.createServer({
root: path.dirname(path.resolve(HTML_FILE)),
});
server.listen(8080);
let result;
try {
result = await minimalcss.minimize({
urls: ["http://0.0.0.0:8080/" + HTML_FILE],
});
} catch (err) {
console.error(err);
throw err;
} finally {
server.close();
}
console.log(result.finalCss);
})();
And the index.html file:
<!DOCTYPE html>
<html>
<head>
<link rel="stylesheet" href="styles.css">
</head>
<body>
<p>Hi @peterbe</p>
</body>
</html>
And the styles.css file:
h1 {
color: red;
}
p,
li {
font-weight: bold;
}
And the output from running that Node script:
p{font-weight:700}
It works!
Suppose all you have is the HTML string and the CSS blob(s)
Suppose all you have is a string of HTML and a list of strings of CSS:
const fs = require("fs");
const path = require("path");
const minimalcss = require("minimalcss");
const httpServer = require("http-server");
const HTML_BODY = `
<p>Hi Peterbe</p>
`;
const CSSes = [
`
h1 {
color: red;
}
p,
li {
font-weight: bold;
}
`,
];
(async () => {
const csses = CSSes.map((css, i) => {
fs.writeFileSync(`${i}.css`, css);
return `<link rel="stylesheet" href="${i}.css">`;
});
const html = `<!doctype html><html>
<head>${csses}</head>
<body>${HTML_BODY}</body>
</html>`;
const fp = path.resolve("./index.html");
fs.writeFileSync(fp, html);
const server = httpServer.createServer({
root: path.dirname(fp),
});
server.listen(8080);
let result;
try {
result = await minimalcss.minimize({
urls: ["http://0.0.0.0:8080/" + path.basename(fp)],
});
} catch (err) {
console.error(err);
throw err;
} finally {
server.close();
fs.unlinkSync(fp);
CSSes.forEach((_, i) => fs.unlinkSync(`${i}.css`));
}
console.log(result.finalCss);
})();
Truth be told, you'll need a good pinch of salt to appreciate that example code. It works but most likely, if you're into web performance so much that you're even doing this, your parameters are likely to be more complex.
Suppose you have your own puppeteer instance
In the first example above, minimalcss will create an instance of puppeteer (e.g. const browser = await puppeteer.launch()) but that means you have less control over which version of puppeteer or which parameters you need. Also, if you have to run minimalcss on a bunch of pages it's costly to have to create and destroy puppeteer browser instances repeatedly.
To modify the original example, here's how you use your own instance of puppeteer:
const path = require("path");
+ const puppeteer = require("puppeteer");
const minimalcss = require("minimalcss");
const httpServer = require("http-server");
const HTML_FILE = "index.html"; // THIS IS YOURS
(async () => {
const server = httpServer.createServer({
root: path.dirname(path.resolve(HTML_FILE)),
});
server.listen(8080);
+ const browser = await puppeteer.launch(/* your special options */);
+
let result;
try {
result = await minimalcss.minimize({
urls: ["http://0.0.0.0:8080/" + HTML_FILE],
+ browser,
});
} catch (err) {
console.error(err);
throw err;
} finally {
+ await browser.close();
server.close();
}
console.log(result.finalCss);
})();
Note that this doesn't buy us anything in this particular example. But that's where your imagination comes in!
Conclusion
You can see the code here as a git repo if that helps.
The point is that this might solve some of the chicken-and-egg problem you might have is that you're building your perfect HTML + CSS and you want to perfect it before you ship it.
Note also that there are other ways to run minimalcss other than programmatically. For example, minimalcss-server is minimalcss wrapped in a express server.
Another thing that you might have is that you have multiple .html files that you want to process. The same technique applies but you just need to turn it into a loop and make sure you call server.close() (and optionally await browser.close()) when you know you've processed the last file. Exercise left to the reader?
15 April 2020
0 comments
Node,
JavaScript
tl;dr; No need install or require body-parser and it's important to send the right content-type header.
I know Express has great documentation but I'm still confused about how to receive JSON and/or how to test it from curl. A great deal of confusion comes from the fact that, I think, body-parser used to be a third-party library you had to install yourself to add it to your Express app. You don't. It now gets installed by installing express. E.g.
▶ yarn init -y
▶ yarn add express
▶ ls node_modules/body-parser
HISTORY.md LICENSE README.md index.js lib package.json
Let's work backward. This is how you set up the Express handler:
const express = require("express"); // v4.17.x as of Apr 2020
const app = express();
app.use(express.json());
app.post("/echo", (req, res) => {
res.json(req.body);
});
app.listen(5000);
And, this is how you test it:
▶ curl -XPOST -d '{"foo": "bar"}' -H 'content-type: application/json' localhost:5000/echo
{"foo":"bar"}%
That's it. No need to require("body-parser") or anything like that. And make sure you're sending the content-type: application/json in the curl command.
Things that can go wrong
I kept fumbling around on StackOverflow questions and rummaging the Express documentation until I figured out what mistake I kept doing. So, here's a variant of the handler above, but much more verbose:
app.post("/echo", (req, res) => {
if (req.body === undefined) {
throw new Error("express.json middleware not installed");
}
if (!Object.keys(req.body).length) {
// E.g curl -v -XPOST http://localhost:5000/echo
if (!req.get("content-Type")) {
return res.status(400).send("no content-type header\n");
}
// E.g. curl -v -XPOST -d '{"foo": "bar"}' http://localhost:5000/echo
if (!req.get("content-Type").includes("application/json")) {
return res.status(400).send("content-type not application/json\n");
}
// E.g. curl -XPOST -H 'content-type:application/json' http://localhost:5000/echo
return res.status(400).send("no data payload included\n");
}
// At this point 'req.body' is *something*.
// For example, you might want to `console.log(req.body.foo)`
res.json(req.body);
});
How you treat these things is up to you. For example, an empty JSON data might be OK in your application.
I.e. perhaps curl -XPOST -d '{}' -H 'content-type:application/json' http://localhost:5000/echo might be fine.
An important option
express.json() is a piece of middleware. By default, it has a simple mechanism for bothering to do put .body into the request object. The default configuration is as if you'd typed:
app.use(express.json({
type: 'application/json',
}));
(it's actually a bit more complicated than that)
If you're confident that you'll always be sending JSON to this handler, and you don't want to have to force clients to have to specify the application/json Content-Type you can change this to:
app.use(express.json({
type: '*/*',
}));
Now you'll find that curl -XPOST -d '{"foo": "bar3"}' localhost:5000/ will work fine.
Instead of curl, let's fetch
This code works the same with node-fetch or browser Fetch API.
fetch("http://localhost:5000/echo", {
method: "post",
body: JSON.stringify({ foo: "bar" }),
headers: { "Content-Type": "application/json" },
})
.then((res) => res.json())
.then((json) => console.log(json));
09 April 2020
0 comments
Nginx,
Linux
I knew I didn't want to download the sources to nginx to install it on my new Ubuntu 19.10 server because I'll never have the discipline to remember to keep it upgraded. No, I'd rather just run apt update && apt upgrade every now and then.
Why is this so hard?! All I need is the ability to set brotli_static on; in my Nginx config so it'll automatically pick the .br file if it exists on disk.
These instructions totally helped but here they are specifically for my version (all run as root):
git clone --recursive https://github.com/google/ngx_brotli.git
apt install brotli
apt-get build-dep nginx
# Note the version of which nginx you have installed
nginx -v
# ...which informs which URL to wget
wget https://nginx.org/download/nginx-1.17.9.tar.gz
aunpack nginx-1.17.9.tar.gz
nginx -V 2>&1 >/dev/null | grep -o " --.*" | grep -oP .+?(?=--add-dynamic-module)| head -1 > nginx-1.17.9/build_args.txt
cd nginx-1.17.9/
./configure --with-compat $(cat build_args.txt) --add-dynamic-module=../ngx_brotli
make install
cp objs/ngx_http_brotli_filter_module.so /usr/lib/nginx/modules/
chmod 644 /usr/lib/nginx/modules/ngx_http_brotli_filter_module.so
cp objs/ngx_http_brotli_static_module.so /usr/lib/nginx/modules/
chmod 644 /usr/lib/nginx/modules/ngx_http_brotli_static_module.so
ls -l /etc/nginx/modules
Now I can edit my /etc/nginx/nginx.conf (somewhere near the top) to:
load_module /usr/lib/nginx/modules/ngx_http_brotli_filter_module.so;
load_module /usr/lib/nginx/modules/ngx_http_brotli_static_module.so;
And test that it works:
nginx -t
08 April 2020
0 comments
Node,
Linux
I'm setting up a new Ubuntu (Eoan Ermine) 19.10 server and I noticed that apt install nodejs gives you Node v10 which is an LTS (Long Term Support) version that'll last till April 2021. However, I want Node v12 which is the most recent LTS release as of April 2020.
To install it I used these instructions:
curl -sL https://deb.nodesource.com/setup_12.x | sudo -E bash -
sudo apt-get install -y nodejs
That worked great.
When it finished, it spat out this nice little blurb about how to install yarn:
...
Fetched 7454 B in 1s (12.3 kB/s)
Reading package lists... Done
## Run `sudo apt-get install -y nodejs` to install Node.js 12.x and npm
## You may also need development tools to build native addons:
sudo apt-get install gcc g++ make
## To install the Yarn package manager, run:
curl -sL https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -
echo "deb https://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
sudo apt-get update && sudo apt-get install yarn
By the way, I have no idea what nodejs-mozilla but running apt show nodejs-mozilla yields:
Package: nodejs-mozilla
Version: 12.16.1-0ubuntu0.19.10.1
Priority: optional
Section: universe/javascript
Origin: Ubuntu
Maintainer: Ubuntu Developers <ubuntu-devel-discuss@lists.ubuntu.com>
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Installed-Size: 42.0 MB
Depends: libc6 (>= 2.29), libgcc1 (>= 1:3.4), libstdc++6 (>= 9)
Homepage: http://nodejs.org/
Download-Size: 10.4 MB
APT-Sources: http://mirrors.digitalocean.com/ubuntu eoan-updates/universe amd64 Packages
Description: evented I/O for V8 javascript
Node.js is a platform built on Chrome's JavaScript runtime for easily
building fast, scalable network applications. Node.js uses an
event-driven, non-blocking I/O model that makes it lightweight and
efficient, perfect for data-intensive real-time applications that run
across distributed devices.
.
Node.js is bundled with several useful libraries to handle server
tasks:
.
System, Events, Standard I/O, Modules, Timers, Child Processes, POSIX,
HTTP, Multipart Parsing, TCP, DNS, Assert, Path, URL, Query Strings.
Installing it doesn't add a node executable and I can't find a home page for it. apt can be weird sometimes.
19 February 2020
0 comments
Python,
MacOSX
I'm still working on getting pyenv in my bloodstream. It seems like totally the right tool for having different versions of Python available on macOS that don't suddenly break when you run brew upgrade periodically. But every thing I tried failed with an error similar to this:
python-build: use openssl from homebrew
python-build: use readline from homebrew
Installing Python-3.7.0...
python-build: use readline from homebrew
BUILD FAILED (OS X 10.15.x using python-build 20XXXXXX)
Inspect or clean up the working tree at /var/folders/mw/0ddksqyn4x18lbwftnc5dg0w0000gn/T/python-build.20190528163135.60751
Results logged to /var/folders/mw/0ddksqyn4x18lbwftnc5dg0w0000gn/T/python-build.20190528163135.60751.log
Last 10 log lines:
./Modules/posixmodule.c:5924:9: warning: this function declaration is not a prototype [-Wstrict-prototypes]
if (openpty(&master_fd, &slave_fd, NULL, NULL, NULL) != 0)
^
./Modules/posixmodule.c:6018:11: error: implicit declaration of function 'forkpty' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
pid = forkpty(&master_fd, NULL, NULL, NULL);
^
./Modules/posixmodule.c:6018:11: warning: this function declaration is not a prototype [-Wstrict-prototypes]
2 warnings and 2 errors generated.
make: *** [Modules/posixmodule.o] Error 1
make: *** Waiting for unfinished jobs....
I read through the Troubleshooting FAQ and the "Common build problems" documentation. xcode was up to date and I had all the related brew packages upgraded. Nothing seemed to work.
Until I saw this comment on an open pyenv issue: "Unable to install any Python version on MacOS"
All I had to do was replace the 10.14 for 10.15 and now it finally worked here on Catalina 10.15. So, the magical line was this:
SDKROOT=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk \
MACOSX_DEPLOYMENT_TARGET=10.15 \
PYTHON_CONFIGURE_OPTS="--enable-framework" \
pyenv install -v 3.7.6
Hopefully, by blogging about it you'll find this from Googling and I'll remember the next time I need it because it did eat 2 hours of precious evening coding time.
