Face to face summary 2

1： Realization sleep function .
Wait for the specified time before executing

function spleep1(ms,fun)
{
    
  setTimeout(() => {
    
    fun();
  }, ms);
}
spleep1(1000,()=>{
    
  console.log("132");
})

Case study

2：css The priority of the
a, Different levels of priority ：
!important > Inline style >ID Selectors > Class selectors > label > wildcard > Inherit > Browser default properties
b, Peer priority ：
The later written style in the same level will overwrite the first written style
c, When multiple levels are added up

**3：DNS What is it? ? **
CDN It is to allocate the nearest resource according to the user's location , Users don't need to visit the source station directly when they surf the Internet , It's a visit away from him “ Current ” One CDN node , The term is edge node , In fact, it is a proxy server that caches the content of the source site .
Principle analysis ：
adopt DNS What you get is no longer ip Address , It is a CNAME(Canonical Name ) Alias record , Point to CDN Global load balancing
effect ：
Improve the speed of user access

3:background-size Of cover and content Usage of
background-size:cover; Represents the stretching of the background picture , If you do it on your cell phone , The background picture will be enlarged , The distortion . This is not right
background-size:content; Indicates that the background picture is normally displayed in the content area , stay pc Stretch end will be covered , But the phone normally displays

4: Block-level elements , Inline elements , The difference between inline block elements

5：js Why single threaded

6：commonjs and es6 The difference between modularity

7：