Various methods of creating js objects are described in detail

It is very common to use js objects in JavaScript development, and how do we create js objects? There are many methods, so today we will talk about various methods of creating js objects.

There are several ways to create objects in JavaScript:

1. Use built-in objects

2. Use JSON symbols

3. Custom object construction
   

1. Use built-in objects
The built-in objects available in JavaScript can be divided into two types:
1, JavaScript language native objects (language-level objects), such as String, Object, Function, etc.;
2, JavaScript runtime host objects ( Environment host-level objects), such as window, document, body, etc.

What we mean by using built-in objects is to instantiate a new object through the construction method of the JavaScript language native object. Such as:

var str = new String("实例初始化String"); 
var str1 = "直接赋值的String"; 
var func = new Function("x","alert(x)");//示例初始化func 
var o = new Object();//示例初始化一个Object

2. Use JSON symbols
What is JSON?
JSON (JavaScript Object Notation) Named JavaScript Object, it is a lightweight data exchange format that is easy to read and write, as well as easy to parse and generate. 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 is a version of JavaScript, and 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 most languages ​​understand as an array.

The commonly used creation method is the first one, 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:

• Simple formatted data exchange;

• Easy to people’s reading and writing habits;

• Easy for machine analysis and operation.

In JavaScript, JSON is understood as an object. Through JSON in the form of String, the data can be easily parsed into JavaScript exclusive, and the data can be read and passed. Through JSON, the problem that JavaScript objects cannot be serialized and passed as parameters is solved to a certain extent.

1, simple JSON

{name:"刘德华",age:"25",sex:"男"}

2, the type of JSON value
The value of JSON can be Simple data types, such as numbers, floating point, characters, etc., can also be 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"}}] 
}

3, using JSON in JavaScript
JSON is a JavaScript native format, which means that JSON is processed in JavaScript The data 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 + ")"));

三、自定义对象构造
创建高级对象构造有两种方式：使用“this”关键字构造、使用原型prototype构造。如：

//使用this关键字定义构造的上下文属性 
function Girl() 
{ 
this.name = "big pig"; 
this.age = 20; 
this.standing; 
this.bust; 
this.waist; 
this.hip; 
} 
//使用prototype 
function Girl(){} 
Girl.prototype.name = "big pig"; 
Girl.prototype.age = 20; 
Girl.prototype.standing; 
Girl.prototype.bust; 
Girl.prototype.waist; 
Girl.prototype.hip; 
alert(new Girl().name);

上例中的两种定义在本质上没有区别，都是定义“Girl”对象的属性信息。“this”与“prototype”的区别主要在于属性访问的顺序。如：

function Test() 
{ 
this.text = function() 
{ 
alert("defined by this"); 
} 
} 
Test.prototype.test = function() 
{ 
alert("defined by prototype"); 
} 
var _o = new Test(); 
_o.test();//输出“defined by this”

当访问对象的属性或者方法是，将按照搜索原型链prototype chain的规则进行。首先查找自身的静态属性、方法，继而查找构造上下文的可访问属性、方法，最后查找构造的原型链。 

“this”与“prototype”定义的另一个不同点是属性的占用空间不同。使用“this”关键字，示例初始化时为每个实例开辟构造方法所包含的所有属性、方法所需的空间，而使用“prototype”定义，由于“prototype”实际上是指向父级的一种引用，仅仅是个数据的副本，因此在初始化及存储上都比“this”节约资源。

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