JS callback function

JS callback function (second week)

What is a callback function

In JavaScript, a function can be used as a parameter to another function, which is called a callback function, and the function that takes the callback function as a parameter is called the main function.

callback function Simple notation

Functions that contain callback functions
Function Main (callback) {
....//main function logic.
Callback (A,b,c ...) The main function triggers a certain condition to pass the value to the callback function and executes
}
Call
Main (function callback (A,b,c ...) {
.....//logical handling in callback functions, ...//
})

callback function Scenario Application

Scene: I am 18 years old, ready to find a girlfriend, there are three candidates (girls A, B, C), I confess that the girl will have a period of time to reply to me; I like a girl, but I don't know if a girl also like me, Confession success rate is 0.4, I second like B girl, confession success rate of 0.5, I know girl C very like me, confession into rate of 1, then the question came, who will become my final female ticket?

Scene Simulation: Using MATH.RANDOWM () to generate a random number between [0,1], if this random number small and scale (can indicate the probability of success), then I declare success, with settimeout (), Delay 1000ms, It means the girls need to get back to me for a long time.

Using Java habits to achieve:

functionGetamie(Woman, scale){Woman the girl I confess the probability of success in scale confessionLet temp= Math.Random(); Console.Log(Temp);If(Temp<scale){Console.Log(`${woman}Promise to be my girlfriend '); Temp= Woman;}Else{Console.Log(`${woman}Told me you were a good man.); Temp=False;}SetTimeout(()={Return Temp;},1000);}Call method, calculate who will eventually become my girlfriendIf(!Getamie("Girl A",0.5)){If(!Getamie("Girl B",1) ) {}else {console. Log ( "finally girl B became my girlfriend"  ) }}else{console. Log ( "finally girl a became my girlfriend"  )              /span>           

However, you will find that the result of the implementation is this:

Yes, this is really not what we want, because JavaScript is single-threaded and does not wait until one function finishes executing another function, so writing in this way is not possible, using a callback to implement the mammary gland:

functionGetamie(Woman, scale, callback){Woman the girl I confess the probability of the success of scale confession callback callback function, callback argument for the girl name when the declaration of success, false means to obtain a good witness aLet temp= Math.Random(); Console.Log(Temp);If(Temp<scale){Console.Log(`${woman}Promise to be my girlfriend '); Temp= Woman;}Else{Console.Log(`${woman}Told me you were a good man.); Temp=False;}SetTimeout(()={Callback(Temp);},1000);}Call method, calculate who will eventually become my girlfriendGetamie("Girl A",0.4,(Temp)={If(Temp){Console.Log("Finally, girl a became my girlfriend.");Return;}Else{Getamie("Girl B",0.5,(Temp)={If(Temp){Console.Log("Finally, girl B became my girlfriend.");Return;}Else{Getamie("Girl C",1,(Temp)={if (Temp{console. Log ( "finally girl C became my girlfriend"  ) }else{return;  })  }) }})    /span>                

Look at the effect, refreshed a few times

< finish >
20180803

Play not widely

JS callback function