Unit-2.pptx

JSON Introduction
• JSON: JavaScript Object Notation.
• JSON is a syntax for storing and exchanging
data.
• JSON is text, written with JavaScript object
notation.

Exchanging Data
• When exchanging data between a browser and a
server, the data can only be text.
• JSON is text, and we can convert any JavaScript
object into JSON, and send JSON to the server.
• We can also convert any JSON received from the
server into JavaScript objects.
• This way we can work with the data as JavaScript
objects, with no complicated parsing and
translations.

JSON Syntax
• The JSON syntax is a subset of the JavaScript
syntax.
JSON Syntax Rules
JSON syntax is derived from JavaScript object
notation syntax:
• Data is in name/value pairs
• Data is separated by commas
• Curly braces hold objects
• Square brackets hold arrays

JSON Data - A Name and a Value

JSON - Evaluates to JavaScript Objects

JSON Values
• In JSON, values must be one of the following data types:
• a string
• a number
• an object (JSON object)
• an array
• a boolean
• null
• In JavaScript values can be all of the above, plus any other valid
JavaScript expression, including:
• a function
• a date
• undefined
• In JSON, string values must be written with double quotes:

JSON vs XML
• Both JSON and XML can be used to receive
data from a web server
• XML is used for data storage
• XML is used for data transmission.
• XML and JSON are used extensive in
WebServices.

The following JSON and XML examples both define an
employees object, with an array of 3 employees:

JSON VS XML
JSON is Like XML Because
• Both JSON and XML are "self describing"
(human readable)
• Both JSON and XML are hierarchical (values
within values)
• Both JSON and XML can be parsed and used
by lots of programming languages
• Both JSON and XML can be fetched with an
XMLHttpRequest

JSON VS XML
JSON is Unlike XML Because
• JSON doesn't use end tag
• JSON is shorter
• JSON is quicker to read and write
• JSON can use arrays

JSON VS XML
The biggest difference is:
• XML has to be parsed with an XML parser.
JSON can be parsed by a standard JavaScript
function.

Why JSON is Better Than XML?
• XML is much more difficult to parse than
JSON.
• JSON is parsed into a ready-to-use JavaScript
object

JSON VS XML
For AJAX applications, JSON is faster and easier than
XML:
Using XML
• Fetch an XML document
• Use the XML DOM to loop through the document
• Extract values and store in variables
Using JSON
• Fetch a JSON string
• JSON.Parse the JSON string

JSON Data Types
Valid Data Types
In JSON, values must be one of the following data
types:
a string
a number
an object (JSON object)
an array
a boolean
null

JSON.parse()
• A common use of JSON is to exchange data
to/from a web server.
• When receiving data from a web server, the
data is always a string.
• Parse the data with JSON.parse(), and the data
becomes a JavaScript object.

Parsing Functions
Functions are not allowed in JSON.
If you need to include a function, write it as a string.
You can convert it back into a function later:
Output

JSON.stringify()
• A common use of JSON is to exchange data
• When sending data to a web server, the data
has to be a string.
• Convert a JavaScript object into a string
with JSON.stringify().

JSON Arrays
• Arrays in JSON are almost the same as arrays
in JavaScript.
• In JSON, array values must be of type string,
number, object, array, boolean or null.
• In JavaScript, array values can be all of the
above, plus any other valid JavaScript
expression, including functions, dates,
and undefined.

Arrays in JSON Objects
• Arrays can be values of an object property:

JSON Arrays
• Accessing Array Values
• You access the array values by using the index
number:

JSON.parse()
• common use of JSON is to exchange data
• When receiving data from a web server, the
data is always a string.
• Parse the data with JSON.parse(), and the data
becomes a JavaScript object.

JSON From the Server
• You can request JSON from the server by using
an AJAX request
• As long as the response from the server is
written in JSON format, you can parse the
string into a JavaScript object.

The onreadystatechange Property
• The readyState property holds the status of
the XMLHttpRequest.
• The onreadystatechange property defines a
function to be executed when the readyState
changes.
• The status property and
the statusText property holds the status of the
XMLHttpRequest object.

Parsing Dates
• Date objects are not allowed in JSON.
• If you need to include a date, write it as a
string.
• You can convert it back into a date object
later:

Unit-2.pptx

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