JavaScript attack (eight) JSON

JSON is the syntax for storing and exchanging textual information. Similar to XML.

JSON is smaller, faster, and easier to parse than XML.

What is JSON?

JSON refers to JavaScript Object notation (JavaScript Object Notation), JSON is a lightweight text data Interchange Format, JSON is independent of language (*), JSON is self-descriptive and easier to understand

* JSON uses JAVASCRIPT syntax to describe data objects, but JSON is still independent of language and platform. The JSON parser and the JSON library support many different programming languages.

JSON-Convert to JavaScript object

The JSON text format is syntactically identical to the code that creates the JavaScript object.

Because of this similarity, the JavaScript program can use the built-in eval () function to generate native JavaScript objects with JSON data without a parser.

like XML

JSON is plain text, JSON has a "self-descriptive" (human-readable), JSON has a hierarchy (values exist in values), JSON can be parsed through JavaScript, JSON data can be transmitted using AJAX

compared to the difference between XML

No end tag, shorter, faster read and write, ability to parse using the built-in JavaScript eval () method, use arrays, do not use reserved words

Why use JSON?

For AJAX applications, JSON is faster and easier to use than XML:

using XML

Read the XML document, use the XML DOM to iterate through the document, read the value, and store it in a variable

using JSON

Read the JSON string and process the JSON string with eval ()

JSON syntax is a subset of JavaScript syntax.

JSON Syntax Rules

JSON syntax is a subset of the JavaScript object notation syntax.

Data in name/value pairs, data is separated by commas, curly braces hold the object, square brackets Save the array

JSON name/value pairs

The writing format for JSON data is: name/value pairs.

Name/value pairs include the field name (in double quotation marks), followed by a colon, and then the value:

"FirstName": "John"

This is easy to understand and is equivalent to this JAVASCRIPT statement:

FirstName = "John"

JSON Value

The JSON value can be: Number (integer or floating point), string (in double quotes), logical value (TRUE or FALSE), array (in square brackets), object (in curly braces), null

JSON Object

The JSON object is written in curly braces:

An object can contain multiple name/value pairs:

{"FirstName": "John", "LastName": "Doe"}

This is also easy to understand, and is equivalent to this JAVASCRIPT statement:

FirstName = "John"= "Doe"

JSON Array

The JSON array is written in square brackets:

An array can contain multiple objects:

 
 
1 {
2 "employees": [
3 { "firstName":"John" , "lastName":"Doe" },
4 { "firstName":"Anna" , "lastName":"Smith" },
5 { "firstName":"Peter" , "lastName":"Jones" }
6 ]
7 }

In the example above, the object "Employees" is an array that contains three objects. Each object represents a record of a person (with a first and last name).

JSON uses JavaScript syntax

Because JSON uses JavaScript syntax, there is no need for additional software to handle JSON in JavaScript.

With JavaScript, you can create an array of objects and assign values like this:

 
 
1 var employees = [
2 { "firstName":"Bill" , "lastName":"Gates" },
3 { "firstName":"George" , "lastName":"Bush" },
4 { "firstName":"Thomas" , "lastName": "Carter" }
5 ];

You can access the first item in an array of JavaScript objects like this:

Employees[0].lastname;

The returned content is:

Gates

You can modify the data like this:

Employees[0].lastname = "Jobs";

JSON File

The file type of the JSON file is ". JSON", and the MIME type of the JSON text is "Application/json"

convert JSON Text to JavaScript object

One of the most common uses of JSON is to read the JSON data (as a file or as a HttpRequest) from the Web server, convert the JSON data to a JavaScript object, and then use that data in the Web page.

To make it easier for you to explain, we use strings as input for demonstrations (not files).

JSON Instance-an object from a string

Create a JavaScript string that contains the JSON syntax:

 
var txt = ‘{ "employees" : [‘ +
‘{ "firstName":"Bill" , "lastName":"Gates" },‘ +
‘{ "firstName":"George" , "lastName":"Bush" },‘ +
‘{ "firstName":"Thomas" , "lastName":"Carter" } ]}‘;

Because JSON syntax is a subset of JavaScript syntax, the JavaScript function eval () can be used to convert JSON text to JavaScript objects.

The eval () function uses the JavaScript compiler to parse the JSON text and then generate the JavaScript object. You must enclose the text in parentheses in order to avoid syntax errors:

var obj = eval ("(" + txt + ")");

To use JavaScript objects in a Web page:

 
1 <p>
2 First Name: <span id="fname"></span><br />
3 Last Name: <span id="lname"></span><br />
4 </p>
5 
6 <script type="text/javascript">
7 document.getElementById("fname").innerHTML = obj.employees[1].firstName
8 document.getElementById("lname").innerHTML = obj.employees[1].lastName
9 </script>

JSON Parser

Tip: The eval () function compiles and executes any JavaScript code. This hides a potential security issue.

Using the JSON parser to convert JSON to JavaScript objects is a safer practice. The JSON parser only recognizes JSON text and does not compile the script.

In the browser, this provides native JSON support, and the JSON parser is faster.

Native JSON support is included in newer browsers and the latest ECMAScript (JavaScript) standards.

Web Browser Support	Web Software Support
Firefox (Mozilla) 3.5 Internet Explorer 8 Chrome Opera 10 Safari 4	Jquery Yahoo UI Prototype Dojo ECMAScript 1.5

JavaScript attack (eight) JSON