To brush the video, it's better to see if you have mastered these interview questions. Slowly accumulating a monthly income of more than 10000 is not a dream.

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CSDN Topic challenge No 1 period

• Event details address ：CSDN

• The topic of the competition ： Front end interview book

• Topic description ： Welcome to join the topic creation partners , If I'm not mistaken , I think you should be a front-end person like me . Now the front end is IT More and more important in your career , Has become an indispensable part , Front end technology is also emerging in endlessly , All kinds of Technology 、 Technical frameworks are also pouring out , The difficulty of front-end interview also increases , If we have a front-end interview collection . If you are a candidate ： You can take it easy solo interviewer , If you're the interviewer ： You can torture the candidate to the bone ！
  In short, we all gather our interview experience and learned knowledge here , Form a set of front-end interview Dictionary of the system . Let readers have a great harvest in both interview and study . Let's build a front-end interview dictionary together ！！！

Now let's look at the problem ！！

Topic 1

1. Briefly, you're right HTML Semantic understanding ？

Examination site

Html The understanding of the

answer

Do the right thing with the right label .
html Semantic makes the content of the page structured , Structure is clearer , Easy for browsers 、 Search engine analysis ; Even in the absence of style CSS Also in a document format , And it's easy to read ;
Search engine crawlers also rely on HTML Tag to determine the context and weight of each keyword , Good for SEO;
Make it easier for people who read the source code to block the website , Easy to read, maintain and understand .

At the end

Topic two

2.  Talk to you about MVVM Understanding of development patterns ？

Examination site

Yes MVVM The understanding of the

answer

MVVM It is divided into Model、View、ViewModel The three .
Model Representative data model , Data and business logic are in Model Defined in layer ;
View representative UI View , Responsible for data presentation ;
ViewModel Responsible for monitoring Model Change of data and control of view update , Dealing with user interaction ;
Model and View There is no direct connection , But through ViewModel To make contact ,Model and ViewModel There is a two-way data binding relationship between . So when Model When the data in is changed, it will trigger View Layer refresh ,View The data changed due to user interaction will also be in Model Medium sync .
This pattern implements Model and View Automatic data synchronization , So developers just need to focus on data maintenance operations , And you don't have to operate it yourself dom

Topic three

4.BFC What is it? ？

Examination site

html and css Mixed knowledge

answer

BFC namely Block Formatting Contexts ( Block level formatting context ), It belongs to the ordinary stream , namely ： The element follows its position in HTML The top-down layout of the middle , In the process , The elements in the row are arranged horizontally , Until the line is full and then the line breaks , Block level elements are rendered as a complete new line , Unless otherwise specified , Otherwise, all elements default to normal stream positioning , It can also be said that , The position of an element in a normal flow is determined by the element in HTML The location in the document determines .
You can put BFC It's a big closed box , In any case, the elements inside the box have been overturned , It doesn't affect the outside .
Trigger... As long as the element satisfies any of the following conditions BFC characteristic

Topic four

5.javascript Of memory ( The garbage ) Recycling mechanism ？

Examination site

 javascript Memory knowledge of

answer

The garbage collector will find out the memory that is no longer in use every once in a while , Then free up memory for it
Generally, mark removal method is used (mark and sweep), When a variable enters the environment, it is marked as entering the environment , Leaving the environment is marked as leaving the environment
The garbage collector will mark all variables stored in memory at runtime , Then remove the variables in the environment and the variables referenced by the variables in the environment （ Closure ）, After all this is done, the variables that are still marked are the ones to be deleted
There are also reference counting methods (reference counting), In low version IE Memory leaks often occur in , Most of the time, because it uses the reference counting method for garbage collection . The strategy of reference counting is to track the number of times each value is used , When a statement is made When you assign a reference type to a variable, the number of references to that value is increased 1, If the value of this variable becomes another , This is worth quoting less 1, When the number of references to this value changes to 0 When the Hou , Indicates that no variables are in use , This value can't be accessed , So you can recycle the space it takes , In this way, the garbage collector will clean up the references when it is running 0 The space occupied by the value of .
stay IE Middle though JavaScript Objects are garbage collected by tag removal , but BOM And DOM Object is garbage collected by reference count , That is to say, as long as it involves BOM And DOM There will be a circular reference problem .

CSDN Topic challenge No 1 period

Topic 5

5. Introduce closures and common scenarios of closures ？

Examination site

 javascript knowledge

answer

A closure is a function that has access to variables in the scope of another function , Common ways to create closures , It's creating another function inside one function
Closures are mainly used to design private methods and variables , The advantage of closures is that they can avoid variable pollution , The disadvantage is that closures are memory resident , Increases memory usage , Improper use can easily cause memory leakage . stay js in , Function is closure , Only functions produce the concept of scope .
Closures have three characteristics ：
Function nested function
Functions can reference external parameters and variables internally
Parameters and variables are not recycled by the garbage collection mechanism
Application scenarios , How to set private variables
Not applicable to the scene ： The function that returns the closure is a very large function
The disadvantage of closures is that they are memory resident , Increases memory usage , Improper use can cause memory leaks
 

I hope all my friends can master it , Don't forget to praise

• Event details address ：CSDN