What are the three ways to create objects in javascript

The method is: 1. Use built-in objects, JavaScript language native objects or runtime host objects; 2. Use JSON notation, using a simple collection of "key/value pairs" or an ordered list of values. ;3. Custom object construction, use the "this" keyword or use the prototype prototype to construct.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

There are several ways to create objects in JavaScript:

(1) Using built-in objects

(2) Using JSON symbols

(3) Custom object construction

1. Using 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 call using built-in objects refers to instantiating a new object through the construction method of the native object of the JavaScript language. For example:

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

(i) What is JSON?

JSON (JavaScript Object Notation) is the naming of JavaScript objects. 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 is understood by most languages ​​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: (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.

1, Simple JSON

{name:"刘德华",age:"25",sex:"男"}

2, Type of JSON value

JSON value can be a simple data type, such as numbers, floating point, characters, etc., also Can 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 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.

(ii) JSON expresses JavaScript objects in string form. For example:

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, and then restore it to the object through the eval method after reaching the destination:

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

3. Custom object construction

There are two ways to create advanced object construction: using the "this" keyword construction and using the prototype prototype construction. For example:

//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);

The two definitions in the above example are essentially the same. They both define the attribute information of the "Girl" object. The difference between "this" and "prototype" mainly lies in the order of attribute access. like:

 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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