What is json? How does javascript create objects with json

What is JSON?

JSON (JavaScript Object Notation) is JavaScript object naming. It is a lightweight data exchange format that is easy to read and write, and is also easy to time. Its parsing and generation. It is based on a subset of "JavaScript Programming Language, Standard ECMA-262 3rd Edition - December 1999". JSON is a completely language-independent text format, making it an ideal format for data exchange.

JSON, as a version of JavaScript, is also provided by a series of languages ​​such as ActionScript, C, C#, ColdFusion, E, Java, JavaScript, ML, ObjectiveCAML, Perl, PHP, Python, Rebol, Ruby, Lua, etc. support, making JSON the preferred solution for Ajax development.

There are two ways to build JSON. One is to use a simple collection of "key/value pairs", which is understood in different languages ​​as objects, records, structures, dictionaries, hash tables, keys List, or associative array, etc. The other uses an ordered list of values, which is understood by most languages ​​as an array.

The commonly used creation method is the first, which is in the form of a "key/value pair" collection. In this form, an object starts with "{" (left bracket) and ends with "}" (right bracket). Each "name" is followed by a ":" (colon), and the "key/value" pairs are separated by a "," (comma).

JSON has the following characteristics: (1) Simple formatted data exchange; (2) Easy for people to read and write; (3) Easy for machine analysis and operation.
In JavaScript, JSON is understood as an object. Through JSON in the form of strings, data can be easily parsed into JavaScript and read and passed. Through JSON, the problem that JavaScript objects cannot be serialized and passed as parameters is solved to a certain extent.

Types of JSON values ​​

JSON values ​​can be simple data types, such as numbers, floating points, characters, etc., or arrays and objects. For example, JSON with an array as the member key value:

{member:[{name:"刘德华"},{name:"郭富城"},{name:"张学友"},{name:"黎明"}]}

{ 
book:[{name:"三国演义"},{name:"西游记"},{name:"水浒传"},{name:"红楼梦"}], 
author:[{name:"罗贯中"},{name:"吴承恩"},{name:"施耐安",{name:"曹雪芹"}}] 
}

Using JSON in JavaScript

JSON is a JavaScript native format, which means that in Processing JSON data in JavaScript does not require any special API or toolkit. JavaScript treats JSON as an object by default.

Pass the object to a variable, for example:

var somebooks = { 
book:[{name:"三国演义"},{name:"西游记"},{name:"水浒传"},{name:"红楼梦"}], 
author:[{name:"罗贯中"},{name:"吴承恩"},{name:"施耐安",{name:"曹雪芹"}}] 
}

Each "key" of JSON is equivalent to a property of the object, such as accessing the first entry in the book, in JavaScript, just You can simply use "somebooks.book[0].name" to get the value of "Romance of the Three Kingdoms".

We can not only convert a JSON string into an object, but also "compile" an object into a JSON string to facilitate the transmission of objects in JavaScript. For example:

var Animals = new Object(); 
Animals.name = "dog"; 
Animals.sex = "Male"; 
Animals.age = "2";

The Animals object cannot be serialized and transmitted. Convert the Animals object into a JSON string, that is, "{name:"dog",sex:"Male",age:"2"}". In this way, the JSON string is passed as a parameter of the HTTP request, thereby achieving the purpose of serializing and transmitting the Animals object.

JSON expresses JavaScript objects in string form. Such as:

var myObject = {nickname:"my girlfried",name:"big pig"};

JSON actually acts as a protocol for mutual conversion between JavaScript objects and strings. Since the "appearance" of JSON can be seen as a string, JSON can play a certain role in JavaScript object transmission. For example, convert the object strObject into a string and then transmit it. After reaching the destination, use the eval method to restore it to the object:

function test (o) 
{ 
alert (o.name) 
} 
var strObject = '{nickname:"my girlfriend",name:"big pig"}'; 
test (eval("(" + strObject + ")"));

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