Json entry, json

Last Update:2015-07-12 Source: Internet

Author: User

Tags javascript eval

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Json entry, json

JSON: JavaScript Object Notation (JavaScriptObjectNotation ).

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

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

Instances used later

{"employees": [{ "firstName":"Bill" , "lastName":"Gates" },{ "firstName":"George" , "lastName":"Bush" },{ "firstName":"Thomas" , "lastName":"Carter" }]}

This employee object is an array containing three employee records (objects.

What is JSON?

JSON refers to the JavaScript Object Notation (JAvaSBytesOBjectNOtation)
JSON is a lightweight text data exchange format.
JSON is independent of the Language *
JSON is self-descriptive and easy to understand.

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

JSON-convert to JavaScript Object

The JSON text format is syntactically the same as the code used to create JavaScript objects.

Because of this similarity, there is no need for a parser. JavaScript programs can use built-in eval () functions to generate native JavaScript objects using JSON data.

<Html> <body> 

 Similar to XML

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

 Differences from XML

 
 
  No end tag
 
  Shorter
 
  Faster read/write speed
 
  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 easier to use than XML:Use XML

 
 
  Read XML documents
 
  Use xml dom to traverse documents cyclically
 
  Read the value and store it in the variable.

 Use JSON

 
 
  Read JSON strings
 
  Use eval () to process JSON strings

 
 
JSON syntax is a subset of JavaScript syntax.JSON syntax rules
JSON syntax is a subset of the syntax of JavaScript Object Notation.

 
 
  Data in name/value pairs
 
  Data is separated by commas (,).
 
  Brackets save objects
 
  Square brackets Save the Array

 JSON name/value pair
JSON data is written in the format of name/value pair.
Name/value pair includes the field name (in double quotation marks), followed by a colon, followed by a value:
"firstName" : "John"
This is easy to understand. It is equivalent to this JavaScript statement:
firstName = "John"JSON Value
The JSON value can be:

 
 
  Number (integer or floating point number)
 
  String (in double quotation marks)
 
  Logical value (true or false)
 
  Array (in square brackets)
 
  Object (in curly brackets)
 
  Null

 JSON object
JSON objects are written in curly brackets:
The object can contain multiple name/value pairs:
{ "firstName":"John" , "lastName":"Doe" }
This is easy to understand and is equivalent to this JavaScript statement:
firstName = "John"lastName = "Doe"JSON Array
JSON array is written in square brackets:
An array can contain multiple objects:
{"employees": [{ "firstName":"John" , "lastName":"Doe" },{ "firstName":"Anna" , "lastName":"Smith" },{ "firstName":"Peter" , "lastName":"Jones" }]}
In the preceding example, the object "employees" is an array containing three objects. Each object represents a record about someone (with a surname and a name.JSON uses JavaScript syntax
Because JSON uses JavaScript syntax, JSON in JavaScript can be processed without additional software.
With JavaScript, you can create an array of objects and assign values as follows:Example
var employees = [{ "firstName":"Bill" , "lastName":"Gates" },{ "firstName":"George" , "lastName":"Bush" },{ "firstName":"Thomas" , "lastName": "Carter" }];
You can access the first entry in the JavaScript Object array as follows:
employees[0].lastName;
The returned content is:
Gates
You can modify the data as follows:
employees[0].lastName = "Jobs";
 
In the following sections, you will learn how to convert JSON text into JavaScript objects.JSON File

 
 
  The JSON file type is ". json"
 
  The MIME type of JSON text is "application/json"

 
 Converts JSON text to JavaScript objects.
One of the most common usage of JSON is to read JSON data (as a file or as HttpRequest) from the web server, convert JSON data into JavaScript objects, and then use the data on the web page.
To make it easier for you, we use strings as input for demonstration (rather than files ).JSON instance-object from string
Create a JavaScript string containing the JSON Syntax:
 
var txt = '{ "employees" : [' +'{ "firstName":"Bill" , "lastName":"Gates" },' +'{ "firstName":"George" , "lastName":"Bush" },' +'{ "firstName":"Thomas" , "lastName":"Carter" } ]}';
 
Because the 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 a JavaScript compiler that parses JSON text and generates JavaScript objects. Text must be enclosed in parentheses to avoid syntax errors:
var obj = eval ("(" + txt + ")");
Use JavaScript objects on a webpage:Example
 
<p>First Name: <span id="fname"></span><br />Last Name: <span id="lname"></span><br /></p><script type="text/javascript">document.getElementById("fname").innerHTML = obj.employees[1].firstNamedocument.getElementById("lname").innerHTML = obj.employees[1].lastName</script>

 
 JSON parser
Tip: the eval () function can compile and execute any JavaScript code. This hides a potential security issue.
It is safer to use the JSON parser to convert JSON into JavaScript objects. The JSON parser can only recognize JSON text, rather than compile scripts.
In the browser, this provides native JSON support, and the JSON parser is faster.
Newer browsers and the latest ECMAScript (JavaScript) standards all contain native support for JSON.

 
 
   
    
    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 
      
    
  

 
 
 
  
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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

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