Interview questions and answers for the second company (2)

1. What are the three main components of a page ？
   html head body
2. The basic attributes of a box model mainly include ？
   margin padding width height border wait
3. 1B = 8 bit
4. The difference between heap and stack ？
   We all know ： In the field of computer , Stacks are two data structures , They can only be at one end ( It's called the top of the stack (top)) Insert and delete data items .

Stack ： Queue priority , fifo ; Release is automatically assigned by the operating system , Stores the parameter values of the function , The value of a local variable, etc . It operates like a stack in a data structure .
Pile up ： First in, then out ; Dynamically allocated space Release is usually assigned by the programmer , If programmers don't release , At the end of the program, the OS Recycling , The distribution method is similar to the linked list .

5.MVC What is it? , What are the differences ？ that MVVM Well ？
MVC It's a use MVC（Model View Controller Model - View - controller ） Design creation Web The pattern of the application ：

• Model（ Model ） Represents the core of the application （ For example, database record list ）.
• View（ View ） Display the data （ Database records ）.
• Controller（ controller ） Process input （ Write database records ）.

MVC The pattern also provides for HTML、CSS and JavaScript Full control of .
Model（ Model ） Is the part of the application that deals with the application's data logic , Usually model objects are responsible for accessing data in the database .
View（ View ） It's the part of the application that handles data display , Usually views are created from model data .
Controller（ controller ） Is the part of the application that handles user interaction , Usually the controller is responsible for reading data from the view , Control user input , And send data to the model .
MVC Layering helps manage complex applications , Because you can focus on one aspect at a time . for example , You can focus on view design without relying on business logic . It also makes it easier to test applications .
MVC Layering also simplifies group development . Different developers can develop views at the same time 、 Controller logic and business logic .

The simplest way to put it is ：

	front end	Back end
M	json xml html data etc.	database Documents, etc.
V	template engine Template fragments, etc	HTML Templates
C	JS Business logic HTTP Request interaction （AJAX,JSONP,WEBSOCKET）	HTTP Request routing Search engine Data analysis File service

Last MVVM yes Model-View-ViewModel（ Model - View - Model view ）. advantage ：

1. Low coupling . View （View） Can be independent of Model Changes and modifications , One ViewModel Can be bound to different "View" On , When View When it changes Model It can be the same , When Model When it changes View It can be the same .
2. Reusability . You can put some view logic in one ViewModel Inside , Let a lot of view Reuse this view logic .
3. Independent development . Developers can focus on the development of business logic and data （ViewModel）, Designers can focus on page design , Use Expression Blend It's easy to design interfaces and generate xaml Code .
4. Testable . The interface is always more difficult to test , And now the test can target ViewModel To write .