Problems in the deconstruction and assignment of objects, comparison between empty strings and undefined

Today, I changed the style of the project , Because the style is manually encapsulated by your tutor , So pass different parameters , There will be different effects , Record a problem encountered today
This is a problematic style

This is the original style

This is the code of the original style


This is the code encapsulated in the component , Think of the parameters passed into the component cType by ’‘ An empty string , according to es6 Object's deconstruction assignment ,cType It should be the default default Well , Later there was a problem with the style , I debugged the breakpoint , Find out cType The value of is ’’, So I went to teacher Ruan Yifeng es6 The official website of the blog reviews the default value of object deconstruction assignment , The original is written like this ,

Only with undefined When strictly equal , Will cause the default value to take effect ,null No way. , An empty string ’' Not good either. , I always thought ‘’ and undefined They are equal. , because ‘’ The comparison will be escaped to false,undefined It will also escape to false( This view is not correct ), But by demo Find out , That's not the truth ,
This is the result of printing

I rely on ,undefined == false was false, I always thought it was true, Because in the previous impression undefined, and unll Can be converted to false, however undefied and null Judgment is not equal to false It's all the time false,
In order to make yourself understand why it is not equal, go to the relevant articles , Finally, I found this article , It makes me feel better ,JavaScript：undefined!=false The solution And == The rules of comparison
Roughly speaking ：undefined It's not equal to false The reason is simple , Because the basic data type is for == When comparing congruently , The rule is to convert the values on both sides into numbers , Let's see if the conversion result numbers are equal ,undefined Into numbers is NAN, So will Number,String,Boolean And undefined When comparing , Always returns false, as for null It's not equal to false Why , Namely null The type of is an object , When the object performs a congruent comparison, it will call valueOf Methods , Returns a scalar , If valueOf Method of does not return a scalar , Will call toString Method , Return scalar （ As for how to call it, please refer to the above article , Very detailed ）, Then convert scalars to numbers for comparison , and null There is no valueOf and toString Method , So it's the return false
Now that we know the problem , That would be a good solution , Because it must be strictly equal to undefined The default value of object deconstruction takes effect , So change the empty string to undefined That's all right. .