Json

JSON
(JavaScript Object Notation)
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What is JSON?
• JSON stands for JavaScript Object Notation
• JSON is a lightweight data-interchange format
• JSON is language independent *
• JSON is "self-describing" and easy to understand
• JSON is a syntax for storing and exchanging data.
• JSON is an easier-to-use alternative to XML.
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JSON Example<!DOCTYPE html>
<html>
<body>
<h2>JSON Object Creation in JavaScript</h2>
<p id="demo"></p>
<script>
var text = '{"name":"John Johnson","street":"Oslo West 16","phone":"555 1234567"}';
var obj = JSON.parse(text);
document.getElementById("demo").innerHTML =
obj.name + "<br>" +
obj.street + "<br>" +
obj.phone;
</script>
</body>
</html> infobizzs.com

 Much Like XML Because
• Both JSON and XML is "self describing" (human readable)
• Both JSON and XML is hierarchichal (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
 Much Unlike XML Because
• JSON doesn't use end tag
• JSON is shorter
• JSON is quicker to read and write
• JSON can use arrays
• The biggest difference is:
XML has to be parsed with an XML parser, JSON can be parsed by a standard JavaScript function.
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Why JSON?
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
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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
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JSON Data - A Name and aValue
• 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:
"firstName":"John"
• JSONValues
• 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 braces)
• null
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JSON Objects
• JSON objects are written inside curly braces.
• Just like JavaScript, JSON objects can contain multiple name/values pairs:
{"firstName":"John", "lastName":"Doe"}
JSON Arrays
• JSON arrays are written inside square brackets.
• Just like JavaScript, a JSON array can contain multiple objects:
"employees":[
{"firstName":"John", "lastName":"Doe"},
{"firstName":"Anna", "lastName":"Smith"},
{"firstName":"Peter","lastName":"Jones"}
]
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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 array of objects and assign data to it, like
this:
var employees = [
{"firstName":"John", "lastName":"Doe"},
{"firstName":"Anna", "lastName":"Smith"},
{"firstName":"Peter","lastName": "Jones"}
];
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JSON HowTo
• 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 by using a string as input (instead of a file).
• JSON Example - Object From String
• Create a JavaScript string containing JSON syntax:
var text = '{ "employees" : [' +
'{ "firstName":"John" , "lastName":"Doe" },' +
'{ "firstName":"Anna" , "lastName":"Smith" },' +
'{ "firstName":"Peter" , "lastName":"Jones" } ]}';
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• JSON syntax is a subset of JavaScript syntax.
• The JavaScript function JSON.parse(text) can be used to convert a JSON text into a
JavaScript object:
var obj = JSON.parse(text);
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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JSON Http Request
• A common use of JSON is to read data from a web server, and display the data in a web page.
• This chapter will teach you, in 4 easy steps, how to read JSON data, using XMLHttp.
• This example reads a menu from myTutorials.txt, and displays the menu in a web page:
<div id="id01"></div>
<script>
var xmlhttp = new XMLHttpRequest();
var url = "myTutorials.txt";
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
var myArr = JSON.parse(xmlhttp.responseText);
myFunction(myArr);
}
}
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xmlhttp.open("GET", url, true);
xmlhttp.send();
function myFunction(arr) {
var out = "";
var i;
for(i = 0; i < arr.length; i++) {
out += '<a href="' + arr[i].url + '">' +
arr[i].display + '</a><br>';
}
document.getElementById("id01").innerHTML = out;
}
</script>
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Example Explained
1: Create an array of objects.
• Use an array literal to declare an array of objects.
• Give each object two properties: display and url.
• Name the array myArray:
myArray
var myArray = [
{
"display": "JavaScriptTutorial",
"url": "http://www.w3schools.com/js/default.asp"
},
{
"display": "HTMLTutorial",
"url": "http://www.w3schools.com/html/default.asp"
},
{
"display": "CSSTutorial",
"url": "http://www.w3schools.com/css/default.asp"
}
]
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2: Create a JavaScript function to display the array.
• Create a function myFunction() that loops the array objects, and display the
content as HTML links:
myFunction()
function myFunction(arr) {
var out = "";
var i;
for(i = 0; i < arr.length; i++) {
out += '<a href="' + arr[i].url + '">' + arr[i].display + '</a><br>';
}
document.getElementById("id01").innerHTML = out;
}
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3: Create a text file
• Put the array literal in a file named myTutorials.txt:
myTutorials.txt
[
{
"display": "JavaScriptTutorial",
"url": "http://www.w3schools.com/js/default.asp"
},
{
"display": "HTMLTutorial",
"url": "http://www.w3schools.com/html/default.asp"
},
{
"display": "CSSTutorial",
"url": "http://www.w3schools.com/css/default.asp"
}
]
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4: Read the text file with an XMLHttpRequest
• Write an XMLHttpRequest to read the text file, and use myFunction() to display
the array:
var xmlhttp = new XMLHttpRequest();
var url = "myTutorials.txt";
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
var myArr = JSON.parse(xmlhttp.responseText);
myFunction(myArr);
}
}
xmlhttp.open("GET", url, true);
xmlhttp.send();
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