Table of contents
1. Simple data types/basic types
Extension: Why is null an object?
2. Complex data types/reference types/object types
Three Object Extensions: Classification of Attributes and Methods
1 custom attribute (own property)
foreword
发现很多小伙伴对js数据类型不是很理解，在本篇文章特别进行了整理分类。
提示：以下是本篇文章正文内容，下面案例可供参考
1. Simple data types/basic types
Simple types are also called basic data types or value types. Put the value itself directly on the stack
1.Number digital type
Contains integer and floating point values Example: 1 0.1
2. String string type
For example: 'Zhang San'
3. Boolean Boolean value type
true、false
4.null
Represents null, is a null pointer
Extension: Why is null an object?
Null: According to the principle that everything is an object, null is an object, but the reason why null (not an object) is judged to be an object type is that "in the initial version of JS, a 32-bit system was used, and the type information of low-order storage variables was used for performance considerations. , the beginning of 000 means an object, but null means all zeros, so it is wrongly judged as an object. Although the current internal type judgment code has changed, this bug has been handed down.
5.undefined
When a variable is declared unassigned, the variable is assigned the value undefined.
6.symbol
ES6 new data type. represents a unique value
2. Complex data types/reference types/object types
Complex types, also called reference types, are placed in the heap first at the stack memory address and then this address points to the data in the heap
1 built-in object
Common built-in objects:
- String(string object);
- Array(array object);
- Date(date object);
- Math(mathematical object);
- Number(number object);
- Function(function object);
2 host object
- BOM - Browser Object Model;
- DOM - Document Object Model;
3 custom objects
The first is a custom object in the form of Object
var variable name=new Object();//object instance (empty object)
The second is a custom object in the form of { } curly braces
Three Object Extensions: Classification of Attributes and Methods
Objects are inseparable from attributes and methods, so what are the types of attributes and methods?
One: attributes
1 custom attribute (own property)
are properties defined directly on the object.
2 Inherited property
is a property defined in the object's prototype object
Two: method
1 static method
This in the static method points to the object that calls it, and the static method can only be called by the class
2 Prototype methods
This in the prototype method points to the instance object, and the prototype method can only be called by the instance
Summarize
Reference type values can add properties and methods, while primitive type values cannot.
The fundamental difference is the storage method in memory, the reference type is stored in the stack, and the basic type is stored in the heap