code sky

 Deep copy is to re-open a new reference address for the variable, which is completely separated from the original, which is equivalent to dividing a new space for itself. Although the content in it is the same, even if one of them is changed, the other is not. will be affected. Shallow copy means that the reference address of the reference type in the stack cannot be changed. The two variables share the same reference address and change the things in the same place. Therefore, the shallow copy causes the change of one variable to cause the same change of the other variable. .

 what is watch? It is an expression or method that monitors changes to a Vue instance. The callback function gets the new value and the old value as arguments, replaced by a function. Simply put: the role of watch can monitor the change of a value, and then call the method that needs to be executed because of the change. You can dynamically view the changes of the instance through watch, and you can also make further operations.