JavaScript Object of Detail

Directory JavaScript Object 1. Definition 2. Classification of Objects 3. Definition of Objects 4. Access to Attributes 5. Add Attributes to Objects 6. Delete Object Attributes 7. Object Root Constructor 8. Detection of Object Attributes 9. Reference and Value Passing 10. Serialization of Objects (Turning Objects into Strings)
11. Enhanced for Loop (for in)

JavaScript object

1. Definition

An object is a reference data type, a container for holding complex data types, and a collection of multiple properties (data) and methods (functions)

It allows dynamic addition and deletion of attributes

2. Classification of objects

(1) Built-in Objects

Objects defined in the ES standard can be used in any implementation of ES

For example: math string number boolean object...

(2) Host object

Objects provided by the running environment of js are mainly provided by browsers at present

For example, BOM DOM

(3) Custom Objects

Objects created by developers themselves

3. Define objects

Object literal

Using object literals, you can specify the properties in an object directly when you create it

Syntax: {Attribute name: Attribute value, Attribute name: Attribute value...}

The attribute name of the literal amount of the object can be quoted or not, and it is recommended not to add it

If you want to use 1 special name, you must put quotation marks

With '{}' as the boundary, attributes are separated from attributes by ',' and attributes are separated from attribute values by ':'

var obj={};

Constructor to create an object

The function called using the new keyword is the constructor constructor

A constructor is a function dedicated to creating objects

When checking 1 object with typeof, object is returned

var obj = new Object();
console.log(typeof obj);

4. Access properties in an object

Point accessor.

o.name      =>  'terry'
o.age       =>   12

Access character

o['name']   =>  'terry'
o['age']    =>  12

If you read an attribute that is not in the object, you will not report an error but return undefined

5. Add attributes to objects

Object. Attribute = attribute value;

o.gender=' Female ';

6. Delete object properties

delete Object. Attributes;

delete o.gender;

7. Object root constructor

All objects directly or indirectly inherit from Object and can call methods in the Object prototype

var o=new Object();
var arr=new Array();

8. Detection of object attributes

in Operator

This operator allows you to check whether an object contains the specified property

If yes, true is returned, and if no, false is returned

Syntax:

"Attribute name" in object

'name' in Obj;

9. Reference passing and value passing

Basic data types use value passing: Basic data types save values directly to the stack area of memory

js The variables in are stored in stack memory 

          Values of basic data types are stored directly in stack memory 

          Value and value are independent, modify 1 A variable does not affect other variables 

var a=123;
var b=a;
a++;
console.log('a='+a);    //124
console.log('b='+b);    //123

Reference data types are passed by reference: The reference address of the reference data type is saved in the stack, and the actual value is saved in the heap, and the reference address points to the space in the heap

Objects are stored in heap memory, and every time a new object is created, a new space will be opened up in heap memory

The variable holds the memory address of the object (reference to the object). If two variables hold the same object reference,

When one variable modifies an attribute, the other variable is also affected

var obj = new Object();
console.log(typeof obj);

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When you compare the values of two basic data types, you compare the values

When comparing two reference data types, it is the memory address of the comparison object

It also returns false if the two objects are 1-mode 1 but have different addresses

var obj = new Object();
console.log(typeof obj);

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10. Serialization of objects (turning objects into strings)

1) Normal conversion

obj.tostring()

2) Convert to an json string

JSON.stringify(obj)

3) Query string

var qs = require ('querystring'); //Introducing node. js Module

qs.stringify(obj) = > name=tom & age=12

11. Enhanced for Loop (for in)

Traversing objects

Syntax:
for (var variable in object) {}
for... There are several properties in the in statement object, and the loop body executes several times

On each execution, 1 attribute name in the object is assigned to the variable

var obj = new Object();
console.log(typeof obj);

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