Filters with JSON keys. In this example the result will be filtered with

number

and

issue_date

keys of

document_details

column

SELECT *
FROM students
WHERE 1 
    AND JSON_EXTRACT(document_details, '$.number') = 8
    AND JSON_EXTRACT(document_details, '$.issue_date') = '2020-05-18'
ORDER BY id DESC

Addition of two integers

5+5; // 10

Multiplication of two integers

5*5; // 25

If we add a number to a string, the number will be converted into a string and the result will be a concatenation of the two strings

5+'12'; // 512

String multiplied by an integer

5*'5'; // 25

Multiplication of a string (but not numeric string) and a number

5*'t'; // NaN

The first operation of the expression is addition and then concatenation

5+5+'2'; // 102

Variable

myName

will be concatenated with the string

let myName = 'Valeri';
console.log('My name is ' + myName + '.');

The result will be:

My name is Valeri.

There are several built-in functions to interact with the user:

alert('Text message');
prompt('What is your name?');
confirm('Do you want to learn JavaScript')

Function

alert

shows a text message

alert('Text message');

Function

prompt

asks the user to input a text. It can be an answer for the question that the function asks the user

prompt('What is your name?');

The function has another optional parameter, which is a default value of the input

prompt('What is your favorite programming language?', 'JavaScript');

Function

confirm

asks the user and waits for the user to accept or cancel

confirm('Do you want to learn JavaScript')

Simple example of the three interactive functions together:

if (confirm('Do you want to learn programming?')) {
    let language = prompt('Choose your favorite programming language: JS, Python, PHP', 'JS');
    alert('You will be redirected to ' + language + " tutorial's page");
    window.location.href = 'https://w3schools.com/'+language;
} else {
    alert('Go waste your time with playing video games')
}

Simple function called

greeting

that shows the following message:

Hello, my name is john

using

alert

built-in function. Then we can call the function by typing the function name followed by parenthesis:

greeting();

function greeting() {
    alert('Hello, my name is john');
}
greeting();

The same function with more flexibility. We pass the parameter

name

to the function, so it can be called for different users. When we call the function, we need to pass a string, as an argument

greeting('John');

function greeting(name) {
    alert('Hello, my name is ' + name);
}
greeting('John');

The same function with several parameters. We added another parameter

age

to the function

function greeting(name, age) {
    alert('Hello, my name is ' + name + ' and I am ' + age + ' years old');
}
greeting('John', 25);

The following function returns value, so that we can use the function in expressions

function doubleMe(number) {
    return 2*number;
}
console.log(3*doubleMe(50));  // 300

We can assign default values to parameters if they are not passed when the function gets called

function aboutMe(profession = 'student', name, city = 'Tbilisi' ) {
    console.log('I am a ' + profession + ' from ' + city + ' and my name is ' + name);
}
aboutMe(undefined, 'Valeri');

Align the flex items at the center of the container:

div {
  display: flex;
  justify-content: center;
}

Align the flex items at the beginning of the container (this is default):

div {
  display: flex;
  justify-content: flex-start;
}

Align the flex items at the end of the container:

div {
  display: flex;
  justify-content: flex-end;
}

Display the flex items with space between the lines:

div {
  display: flex;
  justify-content: space-between;
}

Display the flex items with space before, between, and after the lines:

div {
  display: flex;
  justify-content: space-around;
}

We need to follow the rules if we want our passwords to be strong enough

1. Contains at least 8 characters
2. Contains at least one uppercase letter
3. Contains at least one lowercase letter
4. Contains at least one number
5. Contains at least one special character

Creates array of numbers;

let myFavoriteNumbers = [5, 14, 16, 27]

Creates array of strings

let myFavoriteColors = ['green', 'yellow', 'red']

Creates array of arrays

let myMatrix = [
    [12, 23, 34], 
    [13, 35, 57], 
    [14, 47, 70], 
]

Creates array of objects

let myFavoritePlanets = [
    {name: 'Earth', radius: 6371}, 
    {name: 'Jupiter', radius: 69911}, 
    {name: 'Neptune', radius: 24622, moons: ['Triton', 'Thalassa', 'Nereid', 'Proteus', 'Hippocamp', 'Naiad']}
]

Accessing one of the moons of Neptune

console.log(myFavoritePlanets[2].moons[4])

Creates

myFavoriteNumbers

array

let myFavoriteNumbers = [5, 14, 16, 18]

Adds new item

22

to the array

myFavoriteNumbers.push(22)

Adds the array as a new item to the

myFavoriteNumbers

array

myFavoriteNumbers.push([23, 24])

Adds the object to the array as new item

myFavoriteNumbers.push({firstNumber: 25, secondNumber: 26})

Adds the function to the array as new item

myFavoriteNumbers.push(function(){console.log('I am fired!')})

Adds new string item to the array

myFavoriteNumbers.push('27')

Let's fire the function that we added as an item

myFavoriteNumbers[7]()

After running the function the result will be:

I am fired!

PHP 7.0 + can handle fatal errors without terminating PHP process. It means we can catch the fatal error using

catch

block

try {
    undefinedFunction();
} catch (Error $e) {
    echo 'Fatal error occurred: ' . $e->getMessage();
}

After running the above code on PHP 7+ the result will be:

Fatal error occurred: Call to undefined function undefinedFunction()

If we run the same code on PHP 5.6, we will get the following result:

<br />
<b>Fatal error</b>:  Call to undefined function undefinedFunction() in <b>[...][...]</b> on line <b>5</b><br />