Assigning new object to a variable causes

__destruct

method to call and the old object gets deleted (the same result when we run

unset($old_object)

)

class User {
    public $username;
    public $friends = ['Tom','David'];

    function __construct($name) {
        $this->username = $name;
        print $this->username . "'s object is created'\n";
    }

    function __destruct() {
        print $this->username . "'s object is deleted'\n";
    }
}
$user1 = new User('Tom');
$user1 = new User('George');
unset($user1);
$user2 = new User('David');

echo "\n\n";

After executing the above code the result will be the following:

Tom's object is created'
George's object is created'
Tom's object is deleted'
George's object is deleted'
David's object is created'


David's object is deleted'

In this example when George's object gets created, Tom's object gets deleted immediately. The reason is that we no longer have Tom's object in

$user1

variable

Installs the latest

minor

and

patch

versions of the package but

major

will be the specified version

composer require "vendor/package:2.*"

Activates MySQL console

mysql -u some_user -p

After running the command, we will be required to enter

password

of the mysql user

some_user

After that, MySQL

console

will be activated where we can run MySQL queries

Moves

file.zip

file into

some_folder

folder

sudo mv file.zip some_folder/

In this example

file.zip

file and

some_folder

folder are at the same folder level (they have the same parent folder)

Zips .sql file

db_backup.sql

and locates it to

public_html/

directory

zip -r db_backup.sql public_html/

Unzips the file

zipped.zip

and puts it to the current directory

unzip zipped.zip

Two columns with equal width on all devices and viewport (from

xs

to

xl

)

<div class="row">
    <div class="col">
      1 of 2
    </div>
    <div class="col">
      2 of 2
    </div>
  </div>

Three equal width columns

<div class="row">
    <div class="col">
      1 of 3
    </div>
    <div class="col">
      2 of 3
    </div>
    <div class="col">
      3 of 3
    </div>
  </div>

Shows globally installed modules

npm list --global --depth 0

trait

is kind of solution to the famous

multiple inheritance

problem in PHP. Using traits we can access methods from different traits that we use in our class

class Mobile {
    public function battery() {
        echo 'Battery: MB_06, MF_02, MF_00' . PHP_EOL;
    }
}
trait Laser {
    public function power() {
        echo 'Power: 10 mW' . PHP_EOL;
    }
}
trait Projector {
    public function range() {
        echo 'Range: 2 M' . PHP_EOL;
    }
}
class Galaxy extends Mobile {
    use Laser;
    use Projector;
}

$obj1 = new Galaxy;

$obj1->range();
$obj1->power();
$obj1->battery();

All style attributes can be accessed using the style object of the element. JS

//calling the function in window.onload to make sure the HTML is loaded
window.onload = function() {
    var x = document.getElementById("demo");
    x.style.color = '#6600FF';
    x.style.width = '100px';
};

HTML

<div id="demo" style="width:400px">Some text inside this DIV</div>

Note: All CSS properties can be set and modified using JavaScript. We cannot use dashes (-) in the property names: these are replaced with

camelCase

versions, where the compound words begin with a capital letter. For example: the

background-color

property should be referred to as

backgroundColor

.

If we use several

traits

in the same class, the traits must not have the same method declared

trait Laser {
    public function who() { 
        echo 'I am a Laser' . PHP_EOL; 
    }
}
trait Projector {
    public function who() { 
        echo 'I am a Laser' . PHP_EOL; 
    }
}
class Galaxy {
    use Laser;//, Projector;
    use Projector;
}

Fatal error:

Trait method who has not been applied, because there are collisions with other trait methods on Galaxy