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 data is
written as name/value pairs.
A name/value
pair consists of a field name (in double quotes), followed by a colon, followed
by a value:
Example
"name":"John"
JSON names
require double quotes. JavaScript names don't.
JSON -
Evaluates to JavaScript Objects
The JSON
format is almost identical to JavaScript objects.
In JSON,
keys must be strings, written with double quotes:
JSON
{
"name":"John" }
In
JavaScript, keys can be strings, numbers, or identifier names:
JavaScript
{
name:"John" }
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
{
"name":"John" }
In
JavaScript, you can write string values with double or single quotes:
JavaScript
{
name:'John' }
JSON Uses
JavaScript Syntax
Because JSON
syntax is derived from JavaScript object notation, very little extra software
is needed to work with JSON within JavaScript.
With
JavaScript you can create an object and assign data to it, like this:
Example
var
person = { "name":"John", "age":31,
"city":"New York" };
You can
access a JavaScript object like this:
Example
//
returns John
person.name;
»
It can also
be accessed like this:
Example
//
returns John
person["name"];
»
Data can be
modified like this:
Example
person.name
= "Gilbert";
»
It can also
be modified like this:
Example
person["name"]
= "Gilbert";
»
You will
learn how to convert JavaScript objects into JSON later in this tutorial.
JavaScript
Arrays as JSON
The same way
JavaScript objects can be used as JSON, JavaScript arrays can also be used as
JSON.
You will
learn more about arrays as JSON later in this tutorial.
JSON Files
The file
type for JSON files is ".json"
The MIME
type for JSON text is "application/json"
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