The performance optimization part of the front-end interview (11) 10 small knowledge points per day

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Series Article Directory

The performance optimization part of the front-end interview (1) 10 small knowledge points per day

The performance optimization part of the front-end interview (2) 10 small knowledge points per day

The performance optimization part of the front-end interview (3) 10 small knowledge points per day

The performance optimization part of the front-end interview (4) 10 small knowledge points per day

The performance optimization part of the front-end interview (5) 10 small knowledge points per day

The performance optimization part of the front-end interview (6) 10 small knowledge points per day

The performance optimization part of the front-end interview (7) 10 small knowledge points per day

The performance optimization part of the front-end interview (8) 10 small knowledge points per day

The performance optimization part of the front-end interview (9) 10 small knowledge points per day

The performance optimization part of the front-end interview (10) 10 small knowledge points per day

knowledge points

101. Talk about the relationship between code quality and performance optimization of front-end applications. How do you ensure that performance optimizations don't affect code readability and maintainability?

There is a close relationship between code quality and performance optimization of front-end applications. Although the goal of performance optimization is to improve the loading speed and response time of the application, this does not mean that the readability and maintainability of the code can be sacrificed. Here's how I practice balancing code quality and performance optimization:

1. Code layering and modularization: Code is modularized and layered according to functions, which helps to improve code readability and maintainability. With a clear division of modules, the code is easier to understand and maintain, while also facilitating the application of performance optimizations to specific modules.
2. Comments and Documentation: Provide clear comments and documentation that explain the purpose of the code, design ideas, and special considerations. This helps other developers understand the code, and also provides guidance for future performance optimization efforts.
3. Naming and Standards: Use meaningful naming and consistent coding standards to make code easier to read and maintain. Good naming conventions can make performance-optimizing code changes easier to understand and reduce the risk of introducing bugs.
4. Code review and refactoring: During code review, focus on whether changes for performance optimization are consistent with code quality. If performance optimizations cause code to become complex or difficult to understand, consider refactoring to maintain code quality.
5. Performance testing and monitoring: Before performing performance optimization, perform performance testing to ensure that the optimization measures really produce the expected results. At the same time, application performance is continuously monitored to ensure that performance optimization will not be broken in subsequent code changes.
6. Choose an appropriate optimization method: When performing performance optimization, choose an appropriate optimization method to avoid over-optimization and unnecessary complexity. Always keep your code clean and readable.
7. Use tools and automation: With lint tools and static analysis tools, code quality issues can be automatically detected to ensure optimizations do not introduce potential problems.
8. Continuous learning and training: Encourage team members to continuously learn the best practices of front-end performance optimization and code quality, and maintain an understanding of new technologies and methods, so as to better balance the relationship between the two.

To sum up, code quality and performance optimization go hand-in-hand, and they can be balanced in a project with proper methods and practices. Good code quality contributes to the continued effectiveness of performance optimizations and improves the maintainability and readability of the application.

102. Please summarize what you think are the key points and core principles of front-end performance optimization.

Front-end performance optimization is an important practice in ensuring that a website or application performs at its best in terms of loading speed, response time, and user experience. The following are the key points and core principles of front-end performance optimization in my opinion:

1. Optimize loading speed:
   • Reduce file size: compress, merge, streamline code and resources.
   • Use browser caching: Take advantage of caching to reduce unnecessary network requests.
   • Lazy loading: Load resources on demand, especially for non-critical resources.
2. Improve rendering performance:
   • Minimize repaints and reflows: Avoid frequent DOM operations and use CSS hardware acceleration.
   • Use CSS and JS animations: Avoid performance-impacting JavaScript animations.
   • Leverage the browser rendering pipeline: Improve rendering performance by reducing render-blocking operations.
3. Optimize network requests:
   • Reduce HTTP requests: merge files, use sprites, reduce the number of resources.
   • Use CDN: Utilize content delivery network to accelerate resource loading.
   • Compress resources: use compression techniques such as gzip to reduce file size.
4. Use appropriate image optimization:
   • Choose an appropriate image format: Use an efficient image format like WebP.
   • Adjust image resolution: Adjust the image size according to different devices.
5. Code splitting and on-demand loading:
   • Split the code into modules: load the modules required by the page on demand, reducing the initial loading volume.
   • Using dynamic imports: Implement code splitting and on-demand loading with dynamic imports.
6. Front-end caching strategy:
   • Leverage browser caching: Use appropriate caching headers to cache resources.
   • Implement server-side caching: Use server caching to reduce data requests.
7. Mobile optimization:
   • Responsive Design: Make sure it looks good on different devices.
   • Reduce unnecessary resources: optimize images, fonts and other resources for mobile devices.
8. Continuous Optimization and Monitoring:
   • Regular performance testing: use tools to conduct performance testing to ensure that optimization measures are effective.
   • Monitoring and alerting: Set up performance monitoring and alerting to detect and deal with problems in a timely manner.
9. Avoid over-optimization:
   • Focus on optimizing key paths: Concentrate on optimizing key pages or functions that affect user experience.
   • Avoid unnecessary complexity: Don't introduce hard-to-understand and maintain code for the sake of optimization.
10. Continuous learning and following best practices:
    • Follow the latest trends and best practices in front-end performance optimization.
    • Continuously learn new tools, techniques and methodologies to cope with the ever-changing front-end field.

Combining these points and principles, front-end performance optimization aims to improve user experience, reduce bounce rate, and maintain efficient application performance across various devices and network conditions.

103. When dealing with front-end caching, how do you balance the cache time (TTL) and the validity of cached content to ensure the best performance and experience for users?

When dealing with front-end caching, it is crucial to balance the cache time (TTL, Time-to-Live) and the validity of cached content to ensure the best performance and experience for users. Here are some strategies and practices that can help balance the two:

1. Set different TTLs based on content type: Different types of content may have different frequency of change. For stable static resources (such as style sheets, fonts, etc.), you can set a longer TTL to reduce unnecessary network requests. For dynamic content (such as news, real-time data, etc.), the TTL can be set shorter to ensure that users get the latest information.
2. Rely on the back-end cache policy: If the back-end service has a cache mechanism, the TTL of the front-end cache can be determined according to the settings of the back-end cache. Ensure that the caching policies of the front and back end are consistent to avoid users seeing outdated or inconsistent content.
3. Use versioning: Add a version number or hash to a resource's URL to force the client to re-request the new version when the resource is updated, even if the cache has not expired. This can effectively solve the validity problem of cached content.
4. Real-time data update: For real-time data, a timing or push mechanism can be used to update the cache content in time to ensure that users get the latest information without frequent network requests.
5. Conditional request: Use HTTP conditional requests (such as ETag and Last-Modified) to check whether the resource has expired. If there is no change, return the 304 Not Modified status code, thereby reducing unnecessary data transmission.
6. Manually refresh and clear cache: In specific cases, such as users manually triggering refreshes or resource updates, consider providing the option to manually refresh so that users can get the latest content.
7. Monitoring and alerting: Set up monitoring and alerting mechanisms to detect problems with cached content in a timely manner, such as content updates that are not reflected in the cache in a timely manner.
8. A/B testing and grayscale publishing: When conducting A/B testing or grayscale publishing, ensure that different user groups get the correct version of cached content to avoid confusion or errors.

Taking caching time and content validity into consideration, an appropriate caching strategy can be formulated according to application characteristics and business requirements to achieve the best balance between performance and experience.

104. Talk about how you use responsive image techniques like srcset and sizes attributes to optimize image loading for different screen sizes and devices.

Responsive image technology is one of the important means to optimize image loading for different screen sizes and devices. By using srcsetand sizesattributes, the appropriate image version can be selected according to the device's characteristics and display area, thereby reducing loading time and improving user experience. Here are some practical ways I use responsive image techniques:

1. Choose an appropriate image size: First, provide images of different sizes for different screen sizes and pixel densities. Provide high-resolution images for large screens and appropriate image sizes for small screens to avoid loading overly large images, according to design and layout requirements.
2. Use srcsetattributes: Use attributes in imgtags srcsetto specify image paths of different sizes and resolutions. The browser will select the appropriate image to load according to the characteristics of the device to ensure the best display effect.
3. Use sizesattributes: sizes attributes tell the browser the size of the image in different display areas, helping the browser decide which image size to choose. For example, you can set sizesthe property (max-width: 600px) 100vw, 800pxto indicate that an image with a width of 100% is displayed in a viewport that is less than or equal to 600 pixels, and an image with a width of 800 pixels is displayed otherwise.
4. Consider Viewport Width and Pixel Density: When specifying image dimensions, take viewport width and device pixel density into account. Combining usage sizesand srcsetattributes can provide the best image display effect on different devices.
5. Test and Adjust: Test on different devices and browsers to ensure images load and display correctly in each case. Make adjustments based on test results for the best responsive graphics.
6. Back-end support: Work with the back-end development team to ensure that the server can provide the appropriate version of the image based on the requested device characteristics and screen size. The backend can dynamically generate a suitable image path based on the information in the request header.
7. Use modern formats: Consider using modern image formats such as WebP for better compression and image quality. Specify image paths in srcsetdifferent formats for browsers to choose to load based on support.

In summary, by using srcsetand sizesattributes, as well as appropriate image sizes and formats, you can optimize image loading for different screen sizes and devices, improving page performance and user experience.

105. In front-end development, how to deal with the performance issues of operations and events triggered by user behavior to maintain the smoothness of the application?

In front-end development, it is crucial to deal with performance issues of actions and events triggered by user actions to ensure smooth and responsive applications. Here are some practical ways to deal with these kinds of performance issues:

1. Event delegation: Use event delegation techniques to attach event handlers to a common parent element, rather than each child element having an independent event handler. This can reduce the number of event handlers and improve performance.
2. Throttle and anti-shake: For frequently triggered events (such as scrolling, window adjustment, etc.), you can use throttle and anti-shake (debounce) technologies to limit the trigger frequency of events, avoid excessive function calls, and improve performance.
3. Use Passive Event Listeners: When you listen to scrolling events etc., use passivethe option to tell the browser that your listeners will not prevent scrolling, thus improving the smoothness of scrolling.
4. Lazy loading: For certain operations or content, such as loading pictures, loading more data, etc., lazy loading technology can be used. Only load resources when the user really needs them, reducing initial load time.
5. Avoid blocking: Avoid performing long operations on the main thread, so as not to block the user interface. Place time-consuming operations in Web Workers for processing in the background.
6. Optimize animation and transition effects: use CSS hardware acceleration, requestAnimationFrame and other technologies to optimize animation effects and avoid frequent rearrangement and redrawing operations.
7. Reduce DOM operations: To avoid frequent DOM operations, multiple operations can be combined into one operation, or technologies such as virtual DOM can be used to reduce the number of DOM operations.
8. Performance Analysis and Monitoring: Use tools to analyze and monitor performance, identify potential performance problems, and make optimizations.
9. Asynchronous operations: For some time-consuming operations, such as network requests or calculations, asynchronous operations can be used to avoid blocking the main thread.
10. Regular optimization: Perform performance optimization and testing on a regular basis to ensure that the performance of the application remains at a reasonable level.

Through the comprehensive use of the above technologies and methods, the performance problems of operations and events triggered by user behaviors can be effectively dealt with, and the smoothness and responsiveness of the application can be maintained.

106. Talk about your understanding of the cache hit rate and cache penetration problems in the front-end caching strategy, and how you solve these problems.

The cache hit rate and cache penetration issues in the front-end cache strategy are important concepts closely related to performance optimization. Let me explain these two concepts and how to solve them:

1. Cache Hit Rate: The cache hit rate refers to the ratio of requests obtained from the cache to the total number of requests. A high cache hit rate means that most requests can be obtained from the cache, thereby reducing requests for backend resources and improving performance and efficiency.
2. Cache penetration problem: Cache penetration means that the required data is not found in the cache, causing each request to go through the cache to directly access the backend, which increases the burden on the server and reduces performance. This may be because the requested data has never been cached, or because the data in the cache has expired.

Ways to address these issues include:

• Set an appropriate cache time: Set an appropriate cache time for different types of data. For static resources that do not change frequently, you can set a longer cache time to improve the hit rate. For real-time data, you can set a shorter cache time to avoid penetration problems caused by cache expiration.
• Use hot data preloading: For frequently requested hot data, preloading can be performed in advance before the cache expires to maintain the effectiveness of the cache.
• Bloom Filter: A Bloom filter is a data structure that can be used to determine whether an element exists in a collection. Using Bloom filters in the cache can play a certain defensive role in the cache penetration problem and reduce invalid requests from reaching the backend.
• Null value cache: When a certain data does not exist in the backend, this information can be cached to avoid frequent invalid requests, thereby reducing the burden on the server.
• Request merging: For multiple concurrent requests, the same request can be combined, thereby reducing repeated query operations and improving the cache hit rate.
• Use CDN: For static resources, you can use CDN to distribute, improve the cache hit rate and reduce the load on the server.
• Cache preheating: When the system starts, the cache preheating operation can be performed to load popular data into the cache in advance to improve the cache hit rate.

In general, reasonable caching strategies, using appropriate cache invalidation mechanisms, preloading hotspot data, and using auxiliary data structures can help solve cache hit ratio and cache penetration problems, thereby improving performance and reducing server load.

107. Talk about your learning methods and resources in front-end performance optimization. How do you stay abreast of the latest performance optimization techniques?

When it comes to front-end performance optimization, continuous learning and keeping up with the latest technology is crucial. The following are my methods and resources for learning front-end performance optimization:

1. Online Documentation and Blog: Reading the official documentation, blog posts, and tutorials is fundamental to learning. I often read authoritative resources like MDN Web Docs, Google Developers, Web Fundamentals, etc. to learn about the latest performance optimization techniques and best practices.
2. Books and courses: There are some excellent books and online courses dedicated to front-end performance optimization, such as "Guide to Building High-Performance Websites", "High-Performance JavaScript", etc. These resources often provide in-depth theory and practical examples.
3. Communities and forums: Participate in front-end development communities, such as Stack Overflow, GitHub, etc., and learn experiences and solutions from other developers. Also follow front-end experts on Twitter, who frequently share insights on performance optimization.
4. Real Projects: Applying performance optimization techniques in real projects is one of the best ways to learn. By experimenting with different optimization strategies on your projects, you gain a deep understanding of how these techniques affect performance and learn to make trade-offs and decisions in real-world situations.
5. Tools and testing: Using performance testing tools, such as Lighthouse, WebPageTest, GTmetrix, etc., can help you analyze web page loading performance and provide suggestions for improvement. Use these tools regularly to evaluate your website performance and identify opportunities for optimization.
6. Participate in conferences and seminars: Attend conferences, seminars and training courses related to front-end development to get in touch with the latest trends and technologies in the industry while exchanging experiences with other developers.
7. Subscribe to mailing lists and newsfeeds: Subscribe to some mailing lists or newsfeeds on front-end performance optimization to keep abreast of the latest articles, tools, and resources.
8. Developer Tools: Proficiency in using browser developer tools to analyze page performance, debug performance issues, and try different optimization methods.

In general, through multi-channel learning and practice, I keep understanding and updating the front-end performance optimization technology. Continuous learning and real-world application are key to keeping up in this rapidly changing field.

108. When using AJAX or Fetch in front-end applications, how do you handle concurrent requests and data merging to improve performance?

When using AJAX or Fetch for data requests in front-end applications, handling concurrent requests and data merging is a key performance optimization task. Here are some of my practices for handling concurrent requests and data merging:

1. Batch requests: Combine multiple related requests into one batch request, thereby reducing the number of requests. For example, combine multiple data acquisition requests into one request and return multiple data sets.
2. Use concurrent requests: For independent requests, you can use concurrent send requests to reduce waiting time. In modern browsers, the browser will automatically manage the number of concurrent requests, but you need to be careful not to over-concurrency, so as not to affect performance.
3. Request priority: For important data and resources, different request priorities can be set to ensure that critical data is loaded first. This can be achieved by using Service Worker's prefetching techniques or priority control of XHR requests.
4. Data merging: Data merging is performed on the server side, and the data of multiple requests are combined on the server side and returned together. This reduces network round trips.
5. Use cache: For the same request, you can use browser cache to avoid repeated requests. Using a suitable caching strategy can reduce the number of requests to the backend.
6. Client-side data processing: Data processing and merging are performed on the front end to avoid frequent requests. For example, multiple data sets can be combined and processed at the front end to reduce the number of requests.
7. Paging and infinite scrolling: For a large amount of data, use paging or infinite scrolling to load data in batches to reduce the situation of requesting a large amount of data at one time.
8. Use WebSocket: For real-time data updates, consider using WebSocket to establish a persistent connection and avoid frequent polling requests.
9. CDN and cache: For static resources, you can use CDN to distribute resources, and use browser cache to reduce the number of requests to CDN.
10. Performance monitoring and optimization: use performance monitoring tools, such as Google Analytics, New Relic, etc., to analyze request performance and identify optimization opportunities.

Considering concurrent requests and data merging comprehensively, the efficiency of data loading can be improved while maintaining performance. Different scenarios and requirements may require different optimization strategies, which need to be weighed and selected according to the specific situation.

109. Has Web Accessibility been used in front-end development to improve user experience while ensuring consistency in performance optimization?

Web Accessibility (accessibility) plays a very important role in front-end development, not only to improve user experience, but also to ensure consistency of performance optimization. Here are some of my experiences and practices when using accessibility technologies:

1. Semantic HTML: Use semantic HTML tags to build pages that help screen readers and other assistive technologies better understand page content. Not only does this help with accessibility, it also improves performance because search engines can better understand the page structure.
2. Focus Management: Ensure that the focus on the page is correctly accessed by keyboard navigation. Proper focus management is not only part of accessibility, it can also help keyboard users use your app better.
3. Appropriate ARIA markup: Use ARIA markup (Accessible Rich Internet Applications) to enhance elements that do not have semantic meaning. For example, use attributes such as role, aria-label, aria-describedby, etc. to provide more accessible information.
4. Color Contrast: Make sure there is enough contrast between text and background colors to ensure content can be easily read by users with low vision. This also helps improve the overall user experience.
5. Accessible forms: Make sure form elements have appropriate labels, descriptions, and error messages so screen reader users can fill out and submit forms correctly.
6. Accessibility testing tools: Use accessibility testing tools such as axe, AInspector, etc. to check and fix accessibility issues. These tools can help you identify potential problems and provide solutions.
7. Ongoing accessibility reviews: Incorporate accessibility into every stage of the development process, from design to implementation to testing, to ensure accessibility issues are identified and fixed in a timely manner.

By following accessibility best practices, you can not only improve the user experience, but also ensure consistent performance across different users and devices. Accessibility is a comprehensive consideration that needs to be closely integrated with other aspects such as performance optimization to provide a better user experience.

110. Please share some mistakes or pitfalls that you think are the most common but possibly overlooked in front-end performance optimization.

There are some common but possibly overlooked mistakes or pitfalls when it comes to front-end performance optimization, here are some examples:

1. Uncompressed resources: Resources such as CSS, JavaScript, etc. are not minified and obfuscated before being deployed to production, increasing load times.
2. Excessive third-party scripts: Excessive third-party scripts can cause performance issues as they can block page loads and increase the number of requests.
3. Unoptimized images: Using high-resolution images, unoptimized images have large file sizes and slow page loads.
4. Render-blocking scripts: Putting scripts in the head of the document or putting a large number of scripts in the same place can block the rendering of the page.
5. Excessive redirects: Excessive page redirects can increase page load time and affect user experience.
6. Not using browser cache: Not configuring an appropriate caching policy, resulting in resources needing to be re-downloaded on every request.
7. Large number of HTTP requests: Too many requests for resources on the page, resulting in multiple round-trips, increasing load times.
8. Excessive animations: Excessive or complex animations can cause page stutter and performance issues.
9. Inappropriate font usage: Using too many font variants or custom fonts can increase page load time.
10. Mobile not considered: Performance on mobile devices is not optimized, resulting in a poor mobile user experience.
11. Ignoring front-end framework performance: A front-end framework or library that is not suitable for the project is selected, resulting in performance degradation.
12. Not optimized for mobile web: not using proper image format, not using responsive design, etc., affecting loading speed on mobile web.
13. Failure to perform performance testing: Failure to conduct performance testing before development and deployment may lead to performance problems in actual use.
14. Lack of monitoring and optimization: Lack of performance monitoring and continuous optimization, resulting in problems that cannot be discovered and resolved in a timely manner.

Avoiding these common but possibly overlooked mistakes and pitfalls can help improve front-end performance and provide a better user experience.