react on use of setState

React official reference document, where do the next record

(1) setState grammar

setState (updater, [callback]) 

Analysis: 
　　parameter is a parameter having the form of  updater a function: 
　　Parameter Two optional callback function

　　1, a parameter description

　　

　　Note: Of course, it should not be modified directly. You should use based  state and  props new objects built to represent change. For example, suppose we want According  props.step to increase state:

　　

 

　　updater function received  state and  props are guaranteed up to date. updater return value to  state be shallow merger .

　　

 

　　

　　So we generally use will use its simple syntax

Simple syntax is as follows:
 the this .setState ({ 
   counter 
})

　　2, problem: when to use a parameter object format, when using the format function?

　　The following cases, the cumulative effect of two forms of realization

　　

Object shorthand way is a function of the way 
if the new state is not dependent on the original state ===> using an object mode 
if the new state is dependent on the original state ===> use functions mode 
If you need to get the latest state (after) in setState data, in the second read callback function

　　About dependent and independent, as follows:

　　

 

　　

 

　　3, introduced two parameters

setState () of the second parameter is optional callback function, it will complete merger setState and re-rendering performed after assembly. 
In general, we recommend the use of componentDidUpdate () instead of this method. 
Parameters II: callback function performs timing: after the callback interface status updates and update.

 

　　

　　

 

 

 

 

 

 

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