Basic packaging type

The basic packaging type is a special reference type. Whenever a basic type value is read, a corresponding basic packaging type object will be created in the background, so that properties and methods can be called for subsequent operations.

ECMAScript also provides three basic packaging types: Number, String, and Boolean.

Code status

We often write code like this. Basic type variables can be used as objects to call properties and methods, but this is not a real object, just a variable, so this Why?

1    var str = "hello world";
2     console.log(str.length);     // 11
3     console.log(str.toUpperCase());// HELLO WORLD

In fact, in order to facilitate the operation of basic data type values, the basic data type value in JavaScript will create a corresponding Basic packaging type object## in the background. #, except null and undefined, all basic types have corresponding packaging types.

1. Create an instance of the String type;

2. Call the specified attribute on the instance;

3. Destroy the instance;

1. Create an instance of the String type;

2. Call the specified method on the instance;

3. Destroy this instance;

1 // 执行到第二行时
2 var str = new String("hello world");
3 str.length;
4 str = null;
5 
6 // 执行到第三行时
7 var str = new String("hello world");
8 str.toUpperCase();
9 str = null;

Now do you understand the original basic packaging type? In fact, it is the type corresponding to the basic data type

Note:

It is not that the packaging type provides methods, but that the javascript engine creates instances (objects) of the corresponding basic packaging types in the background )

Whenever a basic type value is read, the background will create a corresponding basic packaging type object such as:

1 var str = new String("hello world");
2  str.length;
3  str = null;

  s='some' s.age='Joel' console.log(s.age);

  s= String('some' s.age='Joel' console.log(s.age);

2. When reading a basic type value, a corresponding basic packaging type object will be created, thus facilitating data operations.
3. Once the object of the basic packaging class is completed, it will be destroyed immediately.

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