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Valeri Tandilashvili's Personal Professional Blog
Results: 1021
Limitations of self::
In this example we are not able to call 
who()
method of the child class 
B
from parent class 
A
class A {
    public static function who() {
        echo __CLASS__;
    }
    public static function test() {
        self::who();
    }
}

class B extends A {
    public static function who() {
        echo __CLASS__;
    }
}

B::test();
The code will call 
who()
method of parent class and print its name 
A
If we need 
test()
to call 
who()
method of child class 
B
from parent class, then we can use 
late static binding
technique. To achieve it, we use 
static
keyword:
class A {
    public static function who() {
        echo __CLASS__;
    }
    public static function test() {
        static::who(); // Here comes Late Static Bindings
    }
}

class B extends A {
    public static function who() {
        echo __CLASS__;
    }
}

B::test();
Categorize students based on their points
Categorizes students based on their points
SELECT *, 
    IF(points>=90, "Brilliant", IF(points>=80, "Gold", IF(points>=60, "Silver", "Lazy"))) AS class
FROM `students`
ORDER BY points DESC
The same result using 
UNION
keyword
SELECT *, 'Brilliant' AS class
FROM `students`
WHERE points >= 90
UNION
SELECT *, 'Gold'
FROM `students`
WHERE points >= 80 
    AND points < 90
UNION
SELECT *, 'Silver'
FROM `students`
WHERE points >= 60 
    AND points < 80
UNION
SELECT *, 'Lazy'
FROM `students`
WHERE points < 60
ORDER BY points DESC
The same result using 
CASE WHEN
conditional statement
SELECT *, 
    CASE 
      	WHEN points>90 THEN "Brilliant"
      	WHEN points>80 THEN "Gold"
      	WHEN points>60 THEN "Silver"
      	ELSE "Lazy"
    END as 'class'
FROM `students`
ORDER BY points DESC
JSONP CODE 
JSONP
is a technique to get data from server without cross-domain issues. JSONP does not use the 
XMLHttpRequest
, instead it uses 
<script>
tag. 
window.onload = function() {
  var s = document.createElement("script");
  s.src = "https://www.w3schools.com/js/demo_jsonp.php";
  document.write(s.outerHTML);
};

// This function will run after the content is fully loaded from the server
function myFunc(myObj) {
  document.write(myObj.name + " is " + myObj.age + " and he lives in " + myObj.city);
}
Requesting a content from another domain can cause problems, due to cross-domain policy. 
<script>
tag does not have this problem and that is the reason why it uses the tag instead of using 
XMLHttpRequest
object. ... Content of the remote 
demo_jsonp.php
file
myFunc({"name":"John", "age":30, "city":"New York"});
toString CODE
If we have a complex object, and we’d like to convert it into a string, to send it over a network, or just to output it for logging purposes, we can use 
toString
method
let user = {
  name: "John",
  age: 30,
  toString() {
    return `{name1: "${this.name}", age1: ${this.age}}`;
  }
};

document.write(user);
// document.write(JSON.stringify(user));
The code above will produce the following result:
{name1: "John", age1: 30}
An interface can extend other interfaces CODE
An interface can extend another interface in the same way that a class can extend another class
Interface IBar {
    public function method3();
}

Interface IArray {
    public function method2();
}

Interface IFoo extends IBar, IArray {
    public function method1();
}

class class1 implements IFoo {
    public function method1() {
        
    }
    public function method2() {
        
    }
    // public function method3() {
        
    // }
}
Class 
class1
implements 
IFoo
interface which extends other two interfaces itself. Because the class has not implemented 
method3
method (commented), then the following error will be generated:
Fatal error:  Class class1 contains 1 abstract method and must therefore be declared abstract or implement the remaining methods (IBar::method3)
more specific selector CODE 
.flex-container > div {
  flex:2;
}
The selector above has class name and tag name, therefore it's more specific than this selector:
.search {
  flex:4;
}
That's why the second selector has no effect in this example. With more specific selector, like this:
.flex-container .search {
  flex:4;
}
the .search item will be twice as wide as the other flex items.
position:absolute CODE
The element is positioned relative to its first positioned (not static) ancestor element
.parent {
    position: relative;
}
.parent h1 {
    position: absolute;
    top: 10px;
}
https://youtu.be/aFtByxWjfLY?t=200
Dynamic JSONP callback
The 
callback function
name is the same as the 
callback
variable passed to the 
URL
https://api.github.com/users/yui?callback=handleJSONP_variable
The content returned from the request:
handleJSONP_variable({"meta": {
  "Content-Type": "application/javascript; charset=utf-8",
  "Cache-Control": "public, max-age=60, s-maxage=60",
  "Vary": "Accept",
  "status": 200,
  ...
}, "data": {
  "login": "yui",
  "name": "YUI Library",
  "company": null,
  "blog": "http://yuilibrary.com/",
  "location": "Sunnyvale, CA",
  "email": null,
  "public_repos": 31,
  ...
}})
Selects elements that has both "cl1" and "cl2" classes
Selects all 
h2
elements that has parent with both 
cl1
and 
cl2
classes
.cl1.cl2 h2{
    color: red;
}
absolute centering using flex properties 
.container {
    display: flex;
    justify-content: center;
    align-items: center;
}
Results: 1021