JavaScript
JSON
JSON is a
format for storing and transporting data.
JSON is
often used when data is sent from a server to a web page.
What is
JSON?
JSON stands
for JavaScript Object Notation
JSON is
lightweight data interchange format
JSON is
language independent *
JSON is
"self-describing" and easy to understand
* The JSON
syntax is derived from JavaScript object notation syntax, but the JSON format
is text only. Code for reading and generating JSON data can be written in any
programming language.
JSON Example
This JSON
syntax defines an employees object: an array of 3 employee records (objects):
JSON Example
{
"employees":[
{"firstName":"John",
"lastName":"Doe"},
{"firstName":"Anna",
"lastName":"Smith"},
{"firstName":"Peter",
"lastName":"Jones"}
]
}
The JSON
Format Evaluates to JavaScript Objects
The JSON
format is syntactically identical to the code for creating JavaScript objects.
Because of
this similarity, a JavaScript program can easily convert JSON data into native
JavaScript objects.
JSON Syntax
Rules
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 data is
written as name/value pairs, just like JavaScript object properties.
A name/value
pair consists of a field name (in double quotes), followed by a colon, followed
by a value:
"firstName":"John"
JSON names
require double quotes. JavaScript names do not.
JSON Objects
JSON objects
are written inside curly braces.
Just like in
JavaScript, objects can contain multiple name/value pairs:
{"firstName":"John",
"lastName":"Doe"}
JSON Arrays
JSON arrays
are written inside square brackets.
Just like in
JavaScript, an array can contain objects:
"employees":[
{"firstName":"John",
"lastName":"Doe"},
{"firstName":"Anna",
"lastName":"Smith"},
{"firstName":"Peter",
"lastName":"Jones"}
]
In the
example above, the object "employees" is an array. It contains three
objects.
Each object
is a record of a person (with a first name and a last name).
Converting a
JSON Text to a JavaScript Object
A common use
of JSON is to read data from a web server, and display the data in a web page.
For
simplicity, this can be demonstrated using a string as input.
First,
create a JavaScript string containing JSON syntax:
var
text = '{ "employees" : [' +
'{
"firstName":"John" , "lastName":"Doe"
},' +
'{
"firstName":"Anna" , "lastName":"Smith"
},' +
'{
"firstName":"Peter" ,
"lastName":"Jones" } ]}';
Then, use
the JavaScript built-in function JSON.parse() to convert the string into a
JavaScript object:
var
obj = JSON.parse(text);
Finally, use
the new JavaScript object in your page:
Example
<p
id="demo"></p>
<script>
document.getElementById("demo").innerHTML
=
obj.employees[1].firstName
+ " " + obj.employees[1].lastName;
</script>
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