1. Alibaba Front End (29 questions)

  1. Used KOA2 middleware
  2. Koa – body principle
  3. Introduce the middleware you have written
  4. Is there a Cluster involved
  5. Introduce pm2
  6. What happens to pm2 when the master dies
  7. How to communicate with MySQL
  8. React declares the cycle and its own understanding
  9. How do I configure the React-router
  10. Dynamic load module for routing
  11. Server rendering SSR
  12. This section describes the history of routes
  13. This section describes the flow of Redux data flow
  14. How does Redux enable communication between multiple components and manage multiple components using the same state
  15. How to split state between multiple components? Each small component has its own state, and there are some common states between them that need to be maintained. How to think about this
  16. Used Redux middleware
  17. How to solve cross-domain problems
  18. Common Http request headers
  19. Mobile adaption 1px problem
  20. Introduction to Flex Layout
  21. In other CSS modes, set the vertical center
  22. Why use transform (why not marginLeft/Top)
  23. What plugin and loader have you used in Webpack
  24. How are plugins in WebPack implemented
  25. How does dev-server run
  26. Project optimization
  27. How is extraction of public files configured
  28. How are security issues handled in the project
  29. How to implement deep copy of this object

2. Netease front-end (26 questions)

  1. What problems does Redux solve
  2. How to upload a file to a breakpoint
  3. Can forms cross domains
  4. What is the difference between Promise and Async
  5. How to handle search requests (anti-shake)
  6. Search request Chinese how to request
  7. Introducing the Observer mode
  8. Introduces the mediator pattern
  9. Where does the distinction between observer and subscription-publish apply
  10. React Optimization
  11. Introduce http2.0
  12. How do concurrent requests work
  13. How to reuse TCP connections with HTTP1.1
  14. Introduce the service worker
  15. This section describes position:sticky in CSS3
  16. How does redux request middleware handle concurrency
  17. Introduction to Promise, exception catching
  18. This section describes the new position property CSS3
  19. Browser event flow
  20. Describes the event broker and its advantages and disadvantages
  21. How to do event proxy in React component
  22. The React component event broker mechanism
  23. Introduce this situation
  24. How does the front end manage routes
  25. How can I solve the problem when ROUTING is used
  26. React How to check and change data

3. Didi (28 Q)

  1. How to switch routes between react and router
  2. What is the difference between a tag and a tag in a React-router
  3. What does it take to jump after the tag default event is disabled
  4. React layer performance optimization
  5. Overall front-end performance improvements fall into several categories
  6. Import {Button} from ‘antd’; import {Button} from ‘antd’
  7. What does Webpack do with dependencies in node_modules when using import
  8. JS asynchronous solution development history and advantages and disadvantages
  9. A request for an Http packet has several parts
  10. Where do cookies go, what do cookies do, and why do they exist
  11. Both cookies and tokens are stored in the header. Why only hijack the former
  12. What are the differences between cookies and sessions
  13. How the React Dom structure changes internally
  14. React has three components: textComponent, composeComponent, and domComponent. How to distinguish data changes when Dom structure changes, how to update, and how to schedule updates. What if there are other tasks in the update
  15. Key is mainly used to solve what kind of problem? Why not use index index (redraw)?
  16. How are asynchronous requests handled in Redux
  17. Redux middleware is something that takes several arguments (Coriolization functions at both ends)
  18. What exactly are the parameters at both ends of a Currie function
  19. How does middleware get store and action, and what does it do with it
  20. How is state injected into components and what is the process from reducer to component
  21. What happens to response.send, Response. rounded, response.json in KOA? Why does the browser recognize that it is a JSON structure or HTML
  22. How does koA-BodyParser parse request
  23. What is the difference between loader and plugin throughout the webpack life cycle
  24. This section describes the AST (Abstract Syntax Tree) Abstract Syntax Tree
  25. How is data passed between Android activities
  26. Android 4.0 to 6.0 WebView js compatibility changes
  27. How do WebViews and native communicate
  28. How to solve cross-domain, have you used Apache and other solutions

4. Toutiao (q 17)

  1. Understanding of async and await, internal principle
  2. So Promise, internal implementation
  3. Remove the floating
  4. Location problem (absolute location, relative location, etc.)
  5. From entering the URL to loading the page
  6. Tcp3 handshake
  7. Which layer does TCP belong to? (1 physical layer > 2 Data link layer > 3 Network layer (IP) > 4 Transport Layer (TCP) > 5 Application layer (HTTP)
  8. Redux’s design philosophy
  9. The process of accessing Redux
  10. The process of binding connect
  11. Connect the principle
  12. Webpack introduction
  13. = = and =When is equality used
  14. Bind, call, apply
  15. Understanding of animation
  16. Introduction to prototype chain (does it solve inheritance problems?)
  17. Knowledge of cross domains

5. (24 Q)

  1. Linux 754 introduced
  2. Bubble sort, selection sort, how to optimize bubble sort
  3. What are the advantages and disadvantages of the Transform animation versus directly using left and top to change positions
  4. How to determine if a linked list has a ring
  5. This paper introduces the characteristics of binary search tree
  6. Introduce temporary dead zones
  7. How are maps in ES6 different from native objects
  8. The difference between observer and publish-subscribe
  9. React Asynchronous rendering concepts and introduction to Time Slicing and Suspense
  10. 16.X declares cycle changes
  11. 16. In which lifecycle should props be processed after changes in X
  12. Introduction to pure functions
  13. Front-end performance optimization
  14. PureComponent is different from FunctionComponent
  15. Introduce JSX
  16. How to adapt RN to Android and IOS
  17. Why RN can be drawn as a native component in a native (bundle.js)
  18. Introducing the virtual DOM
  19. How to design a localStorage to ensure the effectiveness of data
  20. Promise.all()
  21. Introduces advanced components
  22. Sum (2, 3) implements the effect of sum(2)(3)
  23. React Performance Optimization
  24. How do two objects compare

6. Digging for money (24 Q)

  1. The prototype of the JS
  2. Variable scope chain
  3. Call, apply, bind
  4. The difference between anti-shake and throttling
  5. This section describes various asynchronous schemes
  6. React lifecycle
  7. Introduction of Fiber
  8. Front-end performance optimization
  9. This section describes DOM tree comparison
  10. The function of keys in React
  11. How to design a state tree
  12. This section describes the CSS and XSRF
  13. HTTP cache control
  14. How are data structures applied in a project
  15. What capabilities does Native provide to RN
  16. How to do engineering optimization
  17. ShouldComponentUpdate to solve what problem
  18. How to solve the problem that the props level is too deep
  19. How does the front end do unit testing
  20. Webpack life cycle
  21. The whole process of webpack packaging
  22. The commonly used plugins
  23. How do I manage pM2 processes? How do I handle a process failure
  24. How to manage processes without PM2

7. Hujiang (23 ask)

  1. This section describes cross-domain browser
  2. How to solve cross-domain problems
  3. How does the JSONP solution need the server to cooperate
  4. What to set up when Ajax occurs across domains (front end)
  5. The process from initiation to formal success of the request after adding CORS
  6. How to Defend against XSRF cross-domain attacks
  7. What do you notice when you use Async
  8. Async has multiple await requests. How can we optimize the request?
  9. What’s the difference between a Promise and Async when it fails
  10. Redux solves a problem in state management that React itself cannot solve
  11. Did Redux do any packaging
  12. React Life cycle: Common life cycle
  13. What does the corresponding life cycle do
  14. In which lifecycle should performance problems be solved
  15. How to optimize performance (load components asynchronously…)
  16. What details can be optimized for writing React
  17. React’s event mechanism (binding an event to a component)
  18. What are the main problems solved by event broker
  19. Which design patterns are used in front-end development
  20. Which features in React/Redux use which design patterns
  21. There are several types of JS variables. What are the differences
  22. JS garbage collection mechanism is what, which is commonly used, how to deal with
  23. How to organize CSS (Webpack)

8. Are you hungry?

  1. Small procedure inside open page how many
  2. How do React child and parent components transfer values
  3. How to Emit the Emit event and what needs to be introduced
  4. React advanced components. What are the differences between React advanced components and regular components
  5. React creates an array of objects. Each child object contains an ID and a name. How do you render all names
  6. In which life cycle
  7. Some of the names do not exist, get through the asynchronous interface, how to do
  8. What is the value of key for rendering? Can index be used? Id or index is better? What loaders are required for the CSS
  9. How to configure js, CSS, AND HTML to be packaged separately into a file
  10. Div vertically and horizontally centered (Flex, absolute positioning)
  11. Two blocks of elements, one left and one right, spaced 10 pixels apart
  12. Fixed up and down, middle scroll layout how to achieve
  13. [1, 2, 3, 4, 5] becomes [1, 2, 3, a, b, 5]
  14. Take the maximum value of the array (ES5, ES6)
  15. Difference between Apply and call
  16. What is the difference between ES5 and ES6
  17. What is the difference between some, every, find, filter, map, and forEach
  18. The array above is randomly evaluated, returning a different value each time
  19. How do I find random numbers from 0 to 5, 95 to 99
  20. How to bind events with 10,000 buttons on a page
  21. How to tell if it is button
  22. Generate 10,000 buttons on the page, and bind events, how to do (JS native manipulation DOM)
  23. What is the index of the loop binding? Why? How to solve it
  24. The page has an input tag and a P tag. If you change the input tag, the P tag will change
  25. Listening to the inp

9. Ctrip (18 questions)

  1. Write two algorithmic problems by hand
  2. React, do not encounter some pits
  3. What you think about closures, why closures
  4. Hand-written array deduplication function
  5. Handwriting array flattening function
  6. Introduce the purpose and nature of promises
  7. What’s the difference between Promise and Callback
  8. React lifecycle

10. Himalayas (30 Q)

  1. Write two algorithmic problems by hand
  2. React, do not encounter some pits
  3. What you think about closures, why closures
  4. Hand-written array deduplication function
  5. Handwriting array flattening function
  6. Introduce the purpose and nature of promises
  7. What’s the difference between Promise and Callback
  8. React lifecycle

11. (33 Q)

  1. What’s the difference between localStorage and cookie
  2. What are the CSS selectors
  3. The box model, and the difference between the standard case and IE
  4. How to achieve high adaptive
  5. Prototype differs from — proto
  6. What is the _construct
  7. How is new implemented
  8. The essence of promise, its strengths and weaknesses
  9. How to adapt H5 mobile phones
  10. Rem vs. Flex (root EM)
  11. Difference between EM and PX
  12. React declaration cycle
  13. How to remove # from URL
  14. What is the difference between a Redux state manager and a variable mounted in a Window
  15. Advantages and disadvantages of Webpack and gulp
  16. How to implement asynchronous loading
  17. How to implement modular packaging (Multi-entry)
  18. Front-end performance optimization (1JS CSS; 2 pictures; 3 Cache preloading; 4 SSR; 5 Add multiple domain names; 6 Load Balancing)
  19. Maximum number of concurrent requests (6)
  20. Why base64 can improve performance, disadvantages
  21. Webp is an image file format
  22. Introduce koa2
  23. How does a Promise come true
  24. Asynchronous request, low version Fetch How low version adaptation
  25. How does Ajax handle cross-domains
  26. How to set CORS
  27. Why does JSONP not support the POST method
  28. Introduction to the Same Origin Policy
  29. Some components used by React
  30. Introduce Immuable
  31. Introduce the principle of redux process
  32. Introducing the prototype chain

12. Micro Doctor (40 questions)

  1. Introduces JS data types, the difference between basic data types and reference data types
  2. Is Array type Object
  3. A. Var a = {name: “front-end development”}; var b = a; B. Var a = {b: 1} c. Var a = {b: {c: 1}
  4. The difference between stack and heap
  5. Difference between stack and heap when garbage collection
  6. There are 100,000 elements in the array, and how long it takes to fetch the first element and the 100,000th element
  7. How are stacks and heaps stored
  8. Closures and why aren’t they cleared
  9. Closure usage scenarios
  10. How to implement asynchronous JS
  11. Asynchronize the entire execution cycle
  12. Three states of Promise
  13. How to implement Async/Await
  14. The difference between a Promise and a setTimeout
  15. Why does JS distinguish between microtasks and macro tasks
  16. Whether the Promise constructor executes synchronously or asynchronously, then
  17. The difference between publish-subscribe and observer patterns
  18. JS execution process is divided into what stages
  19. Difference between lexical scope and this
  20. How do you normally do inheritance
  21. Deep copy and shallow copy
  22. Implementation principle of loadsh deep copy
  23. How is the let block scope implemented in ES6
  24. What happens after setState in React a. why is setState asynchronous by default B. when is setState synchronous
  25. Why there are so many Native (RN) frameworks (virtual DOM) after the emergence of the three major frameworks
  26. What does the virtual DOM mainly do
  27. What is the virtual DOM itself (JS object)

13. Secoo (20 q)

  1. Introduce the features, advantages and disadvantages of Promise
  2. Introduce Redux
  3. How does RN work on both Android and IOS
  4. How does RN call native functions
  5. Introduce the disadvantages of RN
  6. This section describes the sorting algorithm and the principle of fast sorting
  7. The difference between heap and stack
  8. Introduce the closure
  9. What is the core of closures
  10. The five-tier model of the network
  11. Difference between HTTP and HTTPS
  12. HTTPS encryption process
  13. This section describes SSL and TLS
  14. Introducing DNS Resolution
  15. JS inheritance method
  16. Introduction to Garbage Collection
  17. What problem does a cookie reference solve
  18. Difference between cookie and localStorage
  19. How to solve cross-domain problems
  20. Front-end performance optimization

14. Baby Tree (15 Q)

  1. How to organize common components when drawing using Canvas
  2. What’s the difference between formData and native Ajax
  3. So form submission, how does it relate to formData
  4. This section describes the redux access process
  5. What’s the difference between RudUX and global management (data control, data response)
  6. RN and native communication
  7. How is the MVP presentation organized
  8. Introducing asynchronous solutions
  9. How does promise implement then processing
  10. Koa2 Middleware principles
  11. Common Middleware
  12. How does the server do unified state handling
  13. How do you optimize relative path references
  14. Node file lookup priority
  15. What is the difference between NPM2 and NPM3 +

15. Hikvision (15 questions)

  1. Knex Connects to the database in response to a callback
  2. Introducing asynchronous solutions
  3. How do I handle exception catching
  4. How does the project manage modules
  5. Front-end performance optimization
  6. JS inheritance scheme
  7. How do I determine if a variable is an array
  8. How do I swap variables A and B
  9. Event delegation
  10. The Dom structure generated by the tag is an array of classes
  11. Class array and array difference
  12. How does an array of dom classes turn into an array
  13. This section describes single-page applications and multi-page applications
  14. Redux state tree management
  15. This section describes the apis of LocalStorage

16. Mushroom Street (15 Q)

  1. Semantic understanding of HTML
  2. And the difference ****
  3. Understanding closures
  4. Closure usage scenarios in engineering
  5. Introduce this and the prototype
  6. The biggest benefit of using prototypes
  7. React Design
  8. Why does the virtual DOM perform better than the real DOM
  9. React Common communication mode
  10. Redux’s overall workflow
  11. The difference between redux and global objects
  12. Redux data backtracking design idea
  13. Actual scenarios in singleton, factory, observer projects
  14. The use of trees in the project and understanding
  15. Work to harvest

17. Cool Family Music (21 Q)

  1. React lifecycle
  2. React Performance Optimization
  3. Why does adding native events leak memory without removing them
  4. Where else can memory leak
  5. SetInterval points to pay attention to
  6. Why are timers inaccurate
  7. Difference between setTimeout(1) and setTimeout(2)
  8. Introduces macro and micro tasks
  9. What’s the difference between implementing a promise and then
  10. Introduce pureComponet
  11. Introduce the Function Component
  12. The React data flow
  13. Props and state
  14. Introduce the react context
  15. This section describes the differences between class and ES5 classes
  16. Introduces the difference between arrow functions and ordinary functions
  17. Introduce the defineProperty method. When do you need it
  18. The for… In and object.keys
  19. Describes closures and their usage scenarios
  20. Use scenarios using closure privilege functions
  21. What’s the difference between get and Post

18 percent (14 QUESTIONS)

  1. The difference between React15/16. X
  2. What does rerendering render do
  3. Which methods trigger React rerender
  4. What is the difference between the lifecycle of the updates triggered by state and props
  5. SetState is synchronous or asynchronous
  6. Understanding stateless components
  7. Describes the Redux workflow
  8. This section describes ES6 functions
  9. Let, const, and var
  10. Difference between shallow copy and deep copy
  11. Introduces the arrow function this
  12. Introduce Promise and then
  13. Introduction to Quicksort
  14. Algorithm: the first K largest elements

19. Haifeng Education (Q 14)

  1. React, its pros and cons
  2. How to solve the problems encountered in the process of using
  3. What is the philosophy of React (functional programming for page rendering)
  4. What paradigm language is JS (Object-oriented or functional programming)
  5. Koa principle, why koA (Express vs. KOA)
  6. Koa middleware used
  7. Syntax used in ES6
  8. Promise and async/await and callback
  9. Does Promise address asynchrony (where the Promise chain is really powerful)
  10. The difference between a Promise and a setTimeout (Event Loop)
  11. The difference between a process and a thread (a node instance is a process, a node is a single thread, asynchronous through an event loop
  12. This section describes DFS depth-first
  13. Introduce the observer mode
  14. The data structure used in observer mode (no order, a list)