Many developers try to handle change of input value with change or keyup/keydown event listeners. Well, that's not enough.

You can change the value also by:

• dropping selected text,
• copying it to clipboard and right clicking mouse -> Paste.

The correct way to handle it is with input event listnener. You can read about it on MDN. And you might find interesting this StackOverflow post.

Tags:
#input #js #keyup #keydown #change #event-listener #quickie

Just a command to help you backup / archive your server.

sudo rsync -avhe 'ssh -i /home/user/.ssh/id_rsa -p 2222' \
--numeric-ids \
--progress \
admin@your.server.tld:/path/to/your/data/ \
/path/to/local/data/backup/

-a - archive, this is an alias to lots of other options
-v - verbose, so you see what's happenning
-h - human readable numbers
-e - remote shell
--progress - self explanatory
--numeric-ids - don't map UID/GID by user/group name
For more options refer to manual.

In this example we connect with local user SSH key, to non-standard SSH port 2222.

Keep in mind, if you want to keep permissions and ownership, you need to run this command as root. Otherwise owner will be your local user.

Tags:
#rsync #quickie #bash #backup #archive

Another oddity of JavaScript I found. Multiplying decimal numbers can be tricky (or malicious?).

Order of numbers can matter in multiplication.

// order #1
135*1.15*10.5
// = 1630.125

// order #2
1.15 * 10.5 * 135
// = 1630.125

// order #3
10.5 * 1.15 * 135
// = 1630.125

// order #4
10.5 * 135 * 1.15
// = 1630.1249999999998

This can be bad, if you want to round to 2 decimals. For example in financial operations.

(10.5 * 135 * 1.15).toFixed(2)
// "1630.12"

(10.5 * 1.15 * 135).toFixed(2)
// "1630.13"

Boom! One cent difference.
The solution can be adding a pretty small number to the product. For example 0.000001.

(10.5 * 135 * 1.15 + 1e-6).toFixed(2)
// "1630.13"

(10.5 * 1.15 * 135 + 1e-6).toFixed(2)
// "1630.13"

Tags:
#js #decimal #math #multiplication #toFixed #round

If

Today after debugging minified JS code I discovered an interesting way to write ifs:

var i = 0;
var s = 'foo';

if (s === 'bar') {
    i = 1;
}

can also be written:

var i = 0;
var s = 'foo';

(s === 'bar') && (i = 1);

For

Shorthand for for cycle. Not that you should use it like this.

for (var $i = 0, $j = 0; $i < 3, $j < 4; console.log($i * $j), $j+=2, $i++ );

Tags:
#quickie #if #short #for

PHP's difference between static and self.

class Mom
{
    private const DEFAULT_AGE = 21;


    public static function getName(): string
    {
        return 'Alice';
    }
    
    public function tellAge(int $age = self::DEFAULT_AGE): string
    {
        return 'My age is: ' . $age;
    }
    
    public function tellAge2(int $age = self::DEFAULT_AGE): string
    {
        return 'My age is: ' . $age;
    }
    
    public static function tellAge3(): string
    {
        return 'My default age is: ' . self::DEFAULT_AGE;
    }
    
    // this would explode with 'Fatal error: "static::" is not allowed in compile-time constants'
    //public function tellAge4(int $age = static::DEFAULT_AGE): string
    //{
    //    return 'My age is: ' . $age;
    //}
    
    public static function returnInstance(): self
    {
        return new self();
    }
    
    public static function returnInstance2(): self
    {
        return new static();
    }
}

class Child extends Mom
{
    private const DEFAULT_AGE = 1;

    public static function getName(): string
    {
        return 'Bob';
    }
    
    // tell age 1 is not overridden
    
    public function tellAge2(int $age = self::DEFAULT_AGE): string
    {
        return 'My age is: ' . $age;
    }
    
    public static function tellAge3(): string
    {
        return 'My default age is: ' . self::DEFAULT_AGE;
    }
}


$alice = new Mom();
$bob = new Child();

echo '---------------'. PHP_EOL;
echo Mom::getName() . PHP_EOL;
echo Child::getName() . PHP_EOL;

echo '---------------'. PHP_EOL;
echo $alice->tellAge() . PHP_EOL;
echo $bob->tellAge() . PHP_EOL;

echo '---------------'. PHP_EOL;
echo $alice->tellAge2() . PHP_EOL;
echo $bob->tellAge2() . PHP_EOL;

echo '---------------'. PHP_EOL;
echo Mom::tellAge3() . PHP_EOL;
echo Child::tellAge3() . PHP_EOL;

echo '---------------'. PHP_EOL;
echo get_class(Mom::returnInstance()) . PHP_EOL;
echo get_class(Child::returnInstance()) . PHP_EOL;

echo '---------------'. PHP_EOL;
echo get_class(Mom::returnInstance2()) . PHP_EOL;
echo get_class(Child::returnInstance2()) . PHP_EOL;

Output:

---------------
Alice
Bob
---------------
My age is: 21
My age is: 21
---------------
My age is: 21
My age is: 1
---------------
My default age is: 21
My default age is: 1
---------------
Mom
Mom
---------------
Mom
Child

Tags:
#php #static #self

This little post can be handy specially for full-stack devs, who use JS and PHP. PHP being a requirement here.

Do you know what happens when you assign OR-logical expression to a variable? Specifically in PHP, as it acts differently from other languages.

Python:

result = "hello" || "world"
print(result)

JavaScript:

result = 'hello' || 'world';
console.log(result);

In python and javascript the result is "hello".

PHP:

$result = 'hello' || 'world';
echo $result;

But in PHP you get true.
Don't forget about this when you switch contexts or rewrite code to/from PHP.

Tags:
#php #python #js #quickie

What's the difference between <meter> and <progress> and when to use them?

Meter

indicates value in given range. Do not use this for progress indication.
You can set min, max, current value; low, optimum, and high.

Examples are:

• distance (e.g. from your city to other cities),
• height of person,
• grades at school,
• wind strength,
• precipitation,
• temperature,
• similarity when comparing 2 things.

Progress

Indicates completion of a task or process.
Minimum value is 0. Maximum should be given (1 assumed if max attribute isn't present).

Examples are:

• steps in cart,
• file upload,
• multi-step form completion,
• milestone completion (e.g. on Github),
• loading of application.

Uncertainity

If you have a CV, which indicates the level of your skills - which would you choose?

Let's take language level (A1-C2) as an example.

Meter makes sense, because it indicates value from range. If your knowledge of a language is B1, we can express it as something between 33-50%.
The nice thing about meter is also low / high / optimum parameters. So you can set B1 to "optimum" (considering Cx being "high").

Progress might make sense, because you can still be improving yourself. Language levels can be nice 6 steps in progress.
But user visiting your site will probably not see any progress during her/his visit :)
I think progress is generally better if your visitor can see changes in the process. Well, except milestone completion.

I would personally go with meter.

Styling

For styling please refer to some other resource. I find these two to be nice:

• https://css-tricks.com/html5-meter-element/
• https://css-tricks.com/html5-progress-element/

Tags:
#html #semantics #meter #progress

Have you ever gave up solving some server problem and gave temporal non-root access to anybody?
Or shared your hosting with some other person, how is not supposed to run sudo?

If you run Docker, it could be potentially dangerous.

1. Let's assume you were bothered by always having to type sudo when working with Docker.
   So you added your user to docker group (https://askubuntu.com/questions/477551/how-can-i-use-docker-without-sudo#477554).
2. You probably don't run only custom images, which use by default non-root user.
3. And you probably also didn't do ns-mapping of UIDs.

So anybody with access to such your user can run something like:

docker run -it -v /etc:/host/etc alpine:stretch sh

And voila, he now has root access to your /etc directory.

Tags:
#docker #root #sudo

Once again, different programming languages give different results. Now let's focus on rounding negative numbers.

Python + PHP

print(round(-1.5)) # -2
print(round(1.5))  # 2

echo round(-1.5) // -2
echo round(1.5)  // 2

JavaScript

console.debug(Math.round(-1.5)); // -1
console.debug(Math.round(1.5)); // 2

Rounding

There are way more rounding methods that we were taught at school.
I will not explain them here, but rather share links with you:

• http://mathforum.org/library/drmath/view/71202.html
• https://en.wikipedia.org/wiki/Rounding#Round_half_towards_zero
  Enjoy!

This message was edited, firstly I declared JS negative number rounding incorrent. Then after feedback I read about rounding, so now I don't claim it's wrong. I will just say - be careful with different languages, and check them before you engage in any important math.

Edit 2:
In PHP you can specify which rounding method you want to use (well, I should RTFM next time). It's the 3rd parameter to round function.

StackOverflow suggests to always convert to positive number, and then multiply with -1, if it was a negative number.

Tags:
#js #javascript #math #round #quickie

When you want to get notified every half hour how long you are already working, you can use this simple script, run it in terminal.

Notice however, that it won't save your life nor make the time go faster, but at least it will distract you with little pop-ups :)

Here's the code. It's really a one-liner, just broken into lines for better readability.

while [ 1 ]; do \
    notify-send -u low \
    -t 5000 \
    "You are already working: "$(uptime \
    | awk '{print $3}' \
    | sed 's/,//'); \
    sleep $((30*60)); \
done;

Notes:
I tested it on Cinnamon and MATE desktops, where it works. If you use something simpler like IceWM, it might not work.

Tags: #bash

While I was learning Swedish and Esperanto courses on Duolingo, I noticed how they have opposite meanings for words ni and vi.

So I had to look etymology of them on Wiktionary.

Swedish

ni = you (pl.)

From verb suffix -(e)n with pronoun I. From Old-Swedish ī, ir.
I is an archaic form of you. Also in Danish I is still used.

vi = we

From Old Swedish vīr, which comes from Old Norse vér.
Compare also to Norwegian vi, Danish vi, German wir and English we.

Esperanto

ni = we

Originating in romance languages - Italian noi, Spanish nos, French nous and Latin nos.

vi = you (pl.)

Originating in French vous and Italian voi or Russian вы (vy).

Dankon Duolingo kaj Wiktionary!

Sources:

• https://en.wiktionary.org/wiki/ni#Swedish
• https://en.wiktionary.org/wiki/ni#Esperanto
• https://en.wiktionary.org/wiki/vi#Swedish
• https://en.wiktionary.org/wiki/vi#Esperanto

Tags: #languages #duolingo #swedish #esperanto #etymology