JSON
– Introduction
JSON
– JavaScript
Object Notation
*
JSON is lightweight text-data interchange format
*
JSON is language independent
*
JSON is smaller than XML, and faster and easier to parse.
{
“students” : [ {“name”:”sanjeeva”,
“department”:”CSE”},{“name”:”chandima”,
“department”:”IT”} ] }
*
JSON - Evaluates to JavaScript Objects
The
JSON text format is syntactically identical to the code for creating
JavaScript objects., therefore without using a parser, can use the a
JavaScript built-in eval()
function to execute JSON data.
Like
XML
,
*
JSON is plain text
*
JSON is "self-describing" (human readable)
*
JSON is hierarchical (values within values)
*
JSON can be parsed by JavaScript
*
JSON data can be transported using AJAX
Unlike
XML
,
*
No end tag
*
Shorter
*
Quicker to read and write
*
Can be parsed using built-in JavaScript eval()
*
Uses arrays
*
No reserved words
JSON
Syntax Rules
-
JSON
syntax is a subset of the JavaScript object notation syntax:
*
Data is in name/value
pairs
*
Data is separated by commas
*
Curly
braces hold objects
*
Square
brackets hold arrays
JSON
Name/Value Pairs
name
(field name) / value pair
:
"firstName" : "Sanjeeva"
JSON
values can be:
*
A number (integer or floating point)
*
A string (in double quotes)
*
A Boolean (true or false)
*
An array (in square brackets)
*
An object (in curly brackets)
*
null
JSON
Objects
*
JSON objects are written inside curly brackets,
*
Objects can contain multiple name/values pairs:
{
"firstName":"Sanjeeva" , "lastName":"Pathirana",
“age”:30 }
JSON
Arrays
JSON
arrays are written inside square brackets.
An
array can contain multiple objects:
{
"employees":
[
{
"firstName":"Sanjeeva" , "lastName":"Pathirana"
},
{
"firstName":"Sandamali" , "lastName":"Silva"
},
{
"firstName":"Thinuli" , "lastName":"Pathirana"
}
]
}
In
the example above, the object "employees" is an array
containing three objects. Each object is a record with a first name
and a last name.
JSON
Files
*
The file type for JSON files is ".json"
*
The MIME type for JSON text is "application/json"
Converting
a JSON Text to a JavaScript Object
One
of the most common use of JSON is to fetch JSON data from a web
server (as a file or as an HttpRequest), convert the JSON data to a
JavaScript object, and then it uses the data in a web page.
JSON
Parser
The
eval()
function can compile and execute any JavaScript. This
represents a potential security problem.
It
is safer to use a JSON parser to convert a JSON text to a JavaScript
object. A JSON parser will recognize only JSON text and will not
compile scripts.
