GET

- Retrieves data from the server

HEAD

- Retrieves only headers (without the response body)

POST

- Submits data to the server (used to create resources)

PUT

- Updates/Replaces data on the server

PATCH

- Update/Modify data on the server (used to apply partial modifications to a resource)

DELETE

- Deletes data from the server

The third argument of

JSON.stringify(value, replacer, space)

is the number of spaces to use for pretty formatting

let user = {
  name: "John",
  age: 25,
  roles: {
    isAdmin: false,
    isEditor: true
  }
};

document.write('<pre>' + JSON.stringify(user, null, 8) + '</pre>');

It’s fine if we want to send an object over a network. The

space

argument is used exclusively for a nice output. Note: max value of space parameter is

20

The result of the above code:

{
        "name": "John",
        "age": 25,
        "roles": {
                "isAdmin": false,
                "isEditor": true
        }
}

It has 8 spaces for each TAB

HTML forms only support

GET

and

POST

as HTTP request methods. A workaround for this is to tunnel other methods through

POST

by using a

hidden form field

which is read by the server and the request dispatched accordingly

<input type="hidden" name="_method" value="DELETE">

However,

GET

,

POST

,

PUT

and

DELETE

are supported by the implementations of XMLHttpRequest (i.e. AJAX calls) in all the major web browsers (IE, Firefox, Safari, Chrome, Opera)

The symbols: hyphen

-

, under-score

_

and period

.

are allowed in element name. The XML example is valid

<?xml version="1.0" encoding="UTF-8"?>
<student>
   <first-name>George</first-name>
   <phone.mobile>(011) 123-4567</phone.mobile>
   <native_language>English</native_language>
   <city />
</student>

sub-query

used in

SELECT

clause. Calculates student's point in percent based on max points

SELECT
    id,
    first_name,
    points,
    (
        points * 100 /
        (
            SELECT
                MAX(points)
            FROM
                students
        )
    ) AS percent
FROM
    students

sub-query

used in

IF

conditional statement. Highlights the student with title

Highest

which has highest points

SELECT *, 
    IF(points>=90, IF(points=(SELECT MAX(points) FROM students), "Highest", "Brilliant"), "Lazy") AS class
FROM `students`
ORDER BY points DESC

sub-query

used in

FROM

clause. Select liked notes with likes counts and authors

SELECT 
    students.first_name, 
    note_id, 
    notes.note,
    liked_notes.likes_count
FROM (  
    	SELECT 
            note_likes.note_id AS note_id,
            COUNT(note_likes.id) AS likes_count
        FROM note_likes
        GROUP BY note_likes.note_id
    ) AS `liked_notes`
JOIN notes ON liked_notes.note_id = notes.id
JOIN students ON notes.student_id = students.id
ORDER BY likes_count DESC

sub-query

used in

WHERE

clause. Selects all students that have max points

SELECT
    id,
    first_name,
    points
FROM
    students
WHERE
    points = (
        SELECT
            MAX(points)
        FROM
            students
    )

sub-query

used in

INSERT

statement. Before inserting the record,

sub-query

gets

gender_id

based on the provided gender name

INSERT INTO students (
    first_name, 
    last_name, 
    points,
    gender_id
) 
VALUES (
    'ილია', 
    'დავითაშვილი', 
    '84',
    (SELECT id FROM genders WHERE name = 'Male')
)

sub-query

used in

WHERE

clause in

UPDATE

statement. Updates students table based on notes table column

notes.id

UPDATE 
  students 
SET 
  points = points + 1 
WHERE 
  student_id = (
    SELECT 
      student_id 
    FROM 
      notes 
    WHERE 
      notes.id = 1
  )

An object may provide method toJSON for to-JSON conversion. JSON.stringify automatically calls it if available

let room = {
  number: 23,
  toJSON() {
    return this.number;
  }
};

let meetup = {
  title: "Conference",
  room
};

// document.write(JSON.stringify(room));
document.write(JSON.stringify(meetup));

Result of the code above is the following

{"title":"Conference","room":23}

- An element name can contain any alphanumeric characters. Allowed

symbols

in names are the hyphen

-

, under-score

_

, period

.

and digits

0-9

- Names are

case sensitive

, Address, address, and ADDRESS are different names. - Start and end tags of an element must be

the same

. - An element, which is a container, can contain

text

or

elements

<?xml version="1.0" encoding="UTF-8"?>
<student>
   <first-name>George</first-name>
   <phone.mobile>(011) 123-4567</phone.mobile>
   <native_language>English</native_language>
   <city />
</student>

Note: XML element name must not start with

.

,

-

,

digit

The term

CDATA

means,

Character Data

. CDATA is defined as blocks of text that

are not parsed

by the parser, but are otherwise recognized as markup

<?xml version="1.0" encoding="UTF-8"?>
<student>
    <!-- Some comment about the student -->
    <first-name>George</first-name>
    <phone.mobile>(011) 123-4567</phone.mobile>
    <city />
    <description>
        <![CDATA[
            <p>
            <a href="/mylink/article1"><img style="float: left; margin-right: 5px;" height="80" src="/mylink/image" alt=""/></a>
            Author Names
            <br/><em>Date</em>
            <br/>Paragraph of text describing the article to be displayed</p>
        ]]>        
    </description>
</student>

CDATA Start section

- CDATA begins with the nine-character delimiter

<![CDATA[

CDATA End section

- CDATA section ends with

]]>

delimiter

CData section

- Characters inside

CData

section are interpreted as characters, and not as markup. It may contain markup characters

<

,

>

, and

&

, but they are ignored by the XML processor

1. CDATA is still

part of the document

, while a comment is not 2. In CDATA we cannot include the string

]]>

, while in a comment

--

3. CDATA content is visible on the web if we specify

xmlns

attribute as

http://www.w3.org/1999/xhtml

, even if the file is saved as

.xml

<?xml version="1.0" encoding="UTF-8"?>
<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <title>CDATA Example</title>
    </head>
    <body>

        <h2>Using a Comment</h2>
        <div id="commentExample">
            <!--
            You won't see this in the document
            and can use reserved characters like
            < > & "
            -->
        </div>

        <h2>Using a CDATA Section</h2>
        <div id="cdataExample">
            <![CDATA[
            You will see this in the document
            and can use reserved characters like
            < > & "
            ]]>
        </div>

    </body>
</html>

1.

CDATA 

cannot contain the string

]]>

anywhere in the XML document 2.

Nesting

is not allowed in CDATA section