Window.onload event trigger conditions

The window.onload event trigger condition:

1. When all DOM nodes are loaded.
2. All resources (audio, video, pictures, etc.) on the page have been loaded.

The difference between mouseover event and mouseenter event of the mouse

1. Both mouseover and mouseenter are move-in events.
2. Mouseover will trigger bubbling.
3. mouseenter will not trigger bubbling.

Analyze the difference between basic data types and reference data types

1. The data types are divided into 5 simple data types and 1 complex data type, which correspond to basic type values ​​and reference type values, respectively.
2. Basic type value: null undefined string number boolean.
3. Reference type value: object (regular, array, object, function...).

Basic type value characteristics:

1. We can't add properties and methods to basic type values, even if they are added, they are not available.
2. The basic type of comparison is the comparison of values.
3. The basic types of variables are stored in the stack area (stack area refers to the stack memory in the memory), the stack area includes variable identifiers and variable values

Reference type value characteristics:

1. The value of a reference type is mutable, and we can add properties and methods to the reference type.
2. The value of a reference type is an object stored in both stack memory and heap memory. When we access an object, we must first access the address of the stack area and then refer to the value of the heap area.
3. The comparison of reference types is the comparison of references.

Why label semantics?

1. Semantic tags are more readable and facilitate the development and maintenance of the team.
2. Without css, the web page can also show the content structure and code structure well.
3. Regarding SEO (Search Engine Optimization), search engines can better understand the relationship between various parts of a web page, and search for information more accurately and quickly.