The performance optimization part of the front-end interview (5) 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

knowledge points

41. Talk about your understanding of rendering performance optimization. What steps do you take to improve rendering performance when dealing with large datasets or complex UIs?

Rendering performance optimization refers to improving the speed and efficiency of drawing and rendering UI of applications on browsers or mobile devices through various technologies and strategies. Rendering performance optimization is especially important when dealing with large datasets or complex UIs to ensure a smooth user experience and efficient application operation.

Here are some ways to optimize rendering performance, especially for working with large datasets or complex UIs:

1. Virtualization: Use virtualization technologies, such as virtual scrolling and virtual list, to render only the visible parts of the UI elements, reducing the number of elements rendered at one time.

2. Sharded loading: Divide large data sets into multiple chunks, load and render on-demand to avoid performance problems caused by loading large amounts of data at once.

3. Data caching: Use memory or local storage to cache data, reducing unnecessary network requests and data loading.

4. Web Workers: Use Web Workers to perform data processing and calculations in background threads to avoid blocking the UI thread.

5. Use GPU acceleration: Use CSS hardware acceleration and GPU acceleration to improve the rendering efficiency of complex UI.

6. Lazy loading: Lazy loading of UI elements in non-critical parts, loading the core content first, improving the initial loading speed.

7. Lazy loading: Loading and rendering certain parts of the UI only when the user needs it, such as loading images when scrolling into the visible area.

8. Cache rendering results: For static or less-changing UIs, cache the rendering results to avoid repeated calculations and renderings.

9. Using WebAssembly: For complex computing tasks, WebAssembly can be used to improve performance and offload computing tasks from JavaScript to low-level languages.

10. Reduce redrawing and reflow: By optimizing CSS styles and layouts, page redrawing and reflow are reduced to improve rendering performance.

11. Avoid unnecessary rendering: Use shouldComponentUpdate (React) or a similar mechanism to avoid unnecessary UI re-rendering.

12. Analyze performance bottlenecks: Use browser developer tools or performance analysis tools to locate performance bottlenecks and take corresponding measures.

13. Code splitting and asynchronous loading: Split UI components into smaller parts and use asynchronous loading techniques to spread the load of rendering.

In practical applications, the above methods may need to be combined to select the most suitable optimization strategy to improve rendering performance depending on the specific situation. It is important to constantly monitor and test performance to ensure that the optimizations you take are actually having the desired effect.

42. Have you ever encountered JavaScript code that executes for a long time, causing the page to respond slowly? How did you identify and optimize these performance issues?

To identify performance issues:

1. Use performance analysis tools: Use the performance analysis function of browser developer tools to record page performance data and timelines to identify long-running JavaScript code.
2. CPU and memory usage: Monitor CPU and memory usage. High usage for a long time may be a sign of inefficient code execution.
3. Responsive performance indicators: Pay attention to the key performance indicators of the page, such as loading time, first content painting (FCP), largest content painting (LCP), etc. Abnormal delays may be related to long-executing code.
4. User Feedback: Monitor user feedback and behavior. If users report that the page responds slowly, it may be caused by code that executes for a long time.

Optimizing performance issues:

1. Code Review: Carefully review long-running code to find potential performance issues such as loop nests, heavy calculations, and more.
2. Code Analysis Tools: Use tools to analyze performance bottlenecks in your code and identify time-consuming functions and operations.
3. Optimize algorithm and data structure: optimize algorithm and data structure, reduce unnecessary calculation and traversal, and improve code execution efficiency.
4. Asynchronous operations: Convert long-running operations into asynchronous operations to avoid blocking the main thread.
5. Web Workers: For time-consuming calculations, consider using Web Workers, which are executed in background threads without blocking the UI thread.
6. Shard loading: Divide large data sets into small pieces for batch loading and processing, avoiding loading too much data at one time.
7. Code splitting: Split the code into smaller modules and load them on demand, reducing the pressure on the first load.
8. Caching and memoization: Use caching to store intermediate results to avoid repeated calculations, and use memoization technology to optimize recursion and other operations.
9. Avoid synchronous requests: Avoid synchronous network requests and use asynchronous requests to improve page response speed.
10. Testing and Monitoring: Test and monitor optimized code to ensure performance issues are resolved.

Through the above methods, you can identify and optimize long-running JavaScript codes, improve page responsiveness, and provide better user experience.

43. When using third-party libraries or frameworks, how do you ensure that they do not become a performance bottleneck? Have you encountered any incompatibility or conflict issues? Please share your solution.

When using third-party libraries or frameworks, it is very important to ensure that they do not become a performance bottleneck, and it is also necessary to resolve incompatibilities or conflicts. Here are some ways to ensure third-party libraries or frameworks don't impact performance, and to address potential incompatibilities or conflicts:

1. Choose lightweight libraries or load on demand:
   Choose those lightweight, high-performance third-party libraries, and import only the parts you need as much as possible, avoiding importing the entire library. Some libraries provide on-demand loading, which can load required modules as needed.

2. Evaluate performance impact:
   Before integrating a third-party library, conduct performance tests and benchmarks to assess its impact on load times, rendering performance, and more. Use performance analysis tools to monitor performance indicators to ensure that the introduction of the library does not cause performance degradation.

3. Updates and Maintenance:
   Regularly update third-party libraries to the latest versions for performance and security improvements. At the same time, pay attention to the maintenance status and activity of the library, and avoid using libraries that are no longer maintained.

4. Dealing with conflicts and compatibility:
   When introducing a new third-party library, carefully check for potential conflicts and compatibility issues with existing code or other libraries. If conflicts are found, the following solutions may be considered:

• Use a different library or alternative to avoid conflicts.
• Adjust the load order to ensure correct initialization and execution order.
• Consult the documentation and the community for known solutions or workflows.

5. Use modularity and namespaces:
   Use a modular development approach to avoid global scope conflicts. For libraries and components, mechanisms such as namespaces can be used to ensure that different parts of the code do not interfere with each other.

6. Continuous monitoring and testing:
   After introducing third-party libraries, continuous performance monitoring and testing ensure that they do not introduce new performance issues. Regularly check for updates and evolution of the library to ensure performance and compatibility are maintained.

7. Use build tools and Tree Shaking:
   Use build tools (such as Webpack) for code splitting and compression, and use techniques such as Tree Shaking to eliminate unused code and reduce unnecessary burdens.

In summary, proper selection, use, and maintenance of third-party libraries are key to ensuring performance and avoiding conflict issues. Before integrating any library, fully evaluate its performance, compatibility, and maintenance status, while continuously monitoring and testing after integration to ensure application performance and stability.

44. Have you ever used PWA (Progressive Web Apps) on the mobile side? Please describe your experience implementing PWA in your project and its impact on performance and user experience.

PWA (Progressive Web Apps) is a type of web application created using modern web technologies to provide an experience similar to native applications. PWA has the following characteristics:

1. Progressive Enhancement: PWA apps can be incrementally enhanced to work even in browsers that don’t support certain features.
2. Offline access: PWA can continue to provide basic functions when the network is disconnected, and offline access can be achieved by using cache.
3. Fast loading: PWA uses technologies such as Service Worker, which can cache resources and achieve fast loading, providing better performance.
4. Responsive design: PWA can adapt to different devices and screen sizes, providing a good user experience.
5. Installation and desktop icons: Users can add PWAs to their home screens and launch apps through desktop icons, similar to native apps.

Applying PWA to your project can have some significant performance and user experience impacts:

1. Fast loading and offline access: Using Service Worker to cache resources, PWA can load pages offline while providing faster loading speed and improving user experience.

2. Improve user retention: Since PWA can add icons on the home screen, users can access the application more easily, thereby increasing user retention.

3. Save traffic: By caching resources, PWA can reduce network requests and save users' data traffic.

4. No need to download and install: PWA does not need to be downloaded and installed from the app store, and users can directly access it through a browser, which lowers the threshold for users to use apps.

5. Cross-platform support: PWA is not limited by a specific operating system and can run on browsers of different platforms.

However, to successfully implement a PWA, the following points need to be considered:

• Use and configuration of Service Worker: Service Worker is a key technology for offline access and caching, and requires correct configuration and management.
• Security considerations: PWA involves caching sensitive data and needs to ensure data security.
• Browser support: Different browsers have different support for PWA, which needs to be tested and adapted.
• Caching strategy: It is necessary to clarify which resources need to be cached and how to deal with cache expiration.

In conclusion, PWAs can significantly improve mobile performance and user experience, but proper planning, development, and testing are required before application to ensure successful realization of their benefits.

45. Talk about Tree Shaking and Dead Code Elimination of front-end code. How do they help reduce pack size?

Tree Shaking and Dead Code Elimination are key technologies for front-end code optimization, which help reduce packaging volume and improve application performance and loading speed.

Tree Shaking：

Tree Shaking is a term used to remove unused code (invalid code), usually used to describe the removal of modules, functions, variables, etc. that will not be actually used during the build process. It is mainly used to optimize ES6 modular code, based on the static nature of ES6 modules.

The working principle of Tree Shaking is to determine which code is actually referenced through static code analysis, and then delete the unreferenced code from the final packaging result.

Dead Code Elimination：

Dead Code Elimination is a broader concept that refers to the removal of any code that will not be executed, either at compile time or at runtime. This can cover a variety of situations, including unused functions, unvisited branches, code that will never be executed, etc.

How to help reduce pack size:

1. Reduce redundancy: Tree Shaking and Dead Code Elimination can eliminate unused codes and reduce redundancy, thereby reducing the size of the packaged file.
2. Optimize loading speed: Stripping out dead code reduces the amount of content the browser needs to download and parse, resulting in faster page loads.
3. Improve performance: Reducing the packaging size can reduce the parsing time of the browser, thereby improving the performance and response speed of the page.
4. Saving bandwidth: Reducing the package size can reduce the cost of data transmission and save bandwidth, especially for mobile end users.

Using Tree Shaking and Dead Code Elimination:

When using Tree Shaking and Dead Code Elimination, you need to pay attention to the following points:

• Use a build tool that supports ES6 modules, such as Webpack, Rollup, etc.
• Make sure you use ES6 modular import and export syntax in your code.
• Use modern JavaScript syntax and modularity practices, avoiding global variables or code with side effects.

By using Tree Shaking and Dead Code Elimination correctly, you can minimize the packaging size, optimize the front-end code, and improve the performance and user experience of the application.

46. ​​Talk about the relationship between front-end performance optimization and SEO. Have you ever encountered that the search engine ranking of your website has been affected by performance optimization?

There is a close relationship between front-end performance optimization and SEO (Search Engine Optimization), and optimizing front-end performance can directly or indirectly affect a website's search engine ranking. Search engine companies, such as Google, have made it clear that website performance is an important factor in their ranking algorithms. Here are some considerations on how they relate to each other and how to avoid impacting your rankings due to performance optimizations:

relation:

1. Page Loading Speed: Search engines consider page loading speed as one of their ranking factors. Faster page loading speeds improve user experience and reduce bounce rates, which can have a positive impact on rankings.
2. User Experience: Performance optimization can provide a better user experience, including faster response times and smooth interactions, which are critical for search engine rankings.
3. Mobile-first index: Search engines such as Google have adopted a mobile-first index, which ranks websites based on the mobile version of their content. Optimizing mobile performance is critical for SEO.

Performance optimization factors affecting ranking:

1. Page load time: If a website takes too long to load, it can cause search engines to rank it lower in search results because search engines want to provide users with a faster experience.
2. Bounce rate: If a user chooses to return or jump to another website because the loading time is too long, the search engine may think that the content of the website is not suitable for the user, thereby affecting the ranking.
3. Mobile Friendliness: Performance and user experience on mobile devices are critical to SEO as more and more users search on mobile devices.

Avoid optimization issues that affect rankings:

1. Avoid over-optimization: Over-optimization can lead to complex code or excessive scripts, affecting page load speed. Make sure to strike a balance between performance optimization and functionality.
2. Testing and Monitoring: When performing performance optimizations, always test and monitor to ensure that improvements do not affect the speed and user experience of your site.
3. Accessibility: While accessibility is not a direct SEO factor, it is also important for user experience and rankings. Make sure performance optimizations don't affect accessibility.

Overall, front-end performance optimization can have a positive impact on SEO, but must be approached carefully to ensure that the improvements do not affect the speed, user experience, and other critical aspects of your site. Performance optimization and SEO should be comprehensive strategies aimed at providing the best possible user experience and search engine visibility.

47. How to deal with touch events and scrolling performance issues on the mobile terminal? Have you run into compatibility challenges on specific devices or browsers?

Handling touch events and scrolling performance issues on the mobile side is an important task in mobile front-end development to ensure that users have a smooth interactive experience on mobile devices. Here are some ways to deal with these issues and possible compatibility challenges:

Handle touch events:

1. Use native events: Prioritize the use of native touch events, such as touchstart, touchmove, touchendetc., for better performance and reliability.
2. Event delegation: For multiple similar elements, you can use event delegation to bind the event listener to the parent element to reduce the number of event handlers.
3. Avoid excessive event processing: Avoid performing too many calculations or operations in one touch event to prevent blocking the main thread.
4. Prevent default behavior: It may be necessary to use in event handling preventDefault()to prevent the default scrolling behavior, such as avoiding the overall scrolling of the page.

To deal with scrolling performance issues:

1. Hardware Acceleration: Use CSS hardware acceleration, for example transform: translateZ(0), to optimize scrolling performance and make scrolling smoother.
2. Virtual scrolling: For a scrolling list with a large amount of data, virtual scrolling can be implemented, only rendering the content of the visible area, reducing the number of DOM elements.
3. Reduce DOM operations: Try to avoid a lot of DOM operations when scrolling, because DOM operations will trigger reflow and redrawing, which will affect performance.

Compatibility challenges:

1. Different devices and browsers: The compatibility of mobile devices and browsers is quite different, and specific processing and optimization may be required for different devices and browsers.
2. Event triggering sequence: The sequence of event triggering on different devices may be different, and it is necessary to ensure the consistency of the code on different platforms.
3. Underperforming devices: Some older or lower-performance devices may not perform well in handling complex touch events and scrolling.
4. Viewport and resolution: The viewport size and resolution of different devices can also affect scrolling performance and interactive experience.

To address these compatibility challenges, the following measures can be taken:

• Uses modern CSS and JavaScript techniques and follows best practices to ensure consistent behavior across devices and browsers.
• Conduct cross-browser testing and device testing to discover and resolve compatibility issues in a timely manner.
• Use device- or browser-specific polyfills or libraries to address specific compatibility challenges.

In short, touch events and scrolling performance issues on the mobile terminal need to comprehensively consider the factors of hardware, browser and application itself. By using appropriate technologies and optimization strategies, it is possible to provide a smooth interactive experience while ensuring compatibility on different devices.

48. Have you tried using WebAssembly to improve front-end performance? Please share your experiences and insights.

WebAssembly (Wasm for short) is a binary instruction format for running high-performance code in modern web browsers. It allows developers to write code in other languages ​​(such as C, C++, Rust, etc.), compile it into Wasm format, and then run it in the browser to improve front-end performance and execution speed.

Some of the advantages and insights of using WebAssembly include:

1. Improved performance: WebAssembly typically executes faster than traditional JavaScript, especially for tasks that require high-performance computing.
2. Multi-language support: Using WebAssembly, developers can write code in other languages ​​and then compile it into Wasm format, expanding the language choices for front-end development.
3. Code protection: Since Wasm is in a binary format, it is difficult to reverse engineer, which can increase the security of the code.
4. Modularity and code reuse: Using WebAssembly can convert existing code bases into Wasm modules, which promotes modularity and code reuse.
5. Suitable for computing-intensive tasks: For tasks that require a lot of computing, such as games, image processing, etc., using WebAssembly can achieve better performance.

It is important to note that despite its many advantages, WebAssembly is not a solution for every situation. When working with WebAssembly, you may want to consider the following:

• Compatibility: While most modern browsers support WebAssembly, you still need to check the compatibility of the required features, especially on some older browsers.
• Performance advantage: For some simple tasks, using pure JavaScript may be sufficient, and it is not necessarily necessary to introduce WebAssembly.
• Development and maintenance costs: Using WebAssembly requires additional development and maintenance costs, especially if you need to interact with JavaScript code.

In general, WebAssembly is a potential tool that can improve front-end performance, but in actual applications, it is necessary to weigh its advantages and disadvantages according to specific situations, and carefully evaluate whether it is worth introducing.

49. At work, how do you work with back-end engineers or teams to optimize overall performance?

1. Communication and Collaboration:

Establish an open communication channel and regularly communicate with the backend team to share performance issues and optimization strategies. Make sure both parties understand the performance goals and requirements.

2. Performance Monitoring:

Use performance monitoring tools to track application performance metrics, including load times, response times, database queries, and more. Back-end engineers can use these indicators to understand the performance status of the front-end.

3. Data transfer and API design:

Optimizing data transmission is the key to optimizing front-end and back-end performance. Back-end engineers can design efficient APIs to reduce unnecessary data transmission, such as only transmitting required data fields, and avoid excessive data acquisition.

4. Caching strategy:

Coordinate with the backend team and formulate appropriate caching strategies to ensure that both static resources and dynamic data can be effectively cached to reduce unnecessary requests.

5. Database optimization:

Back-end engineers can optimize database queries, indexes, and data structures to improve data retrieval efficiency, thereby reducing back-end response times.

6. Image and Media Optimization:

Work with back-end engineers to optimize the compression and transmission of images and media resources to reduce front-end loading volume.

7. Lazy loading and chunked loading:

Work with back-end engineers to implement lazy loading and chunked loading strategies to ensure that pages and resources are loaded only when needed, improving initial loading speed.

8. Error handling and status codes:

Work with the backend team to define error handling and status codes to ensure that the frontend can properly handle errors and status information returned by the backend.

9. Front-end and back-end separation and API documentation:

Ensure that there is a clear API document, and clarify the responsibilities and interfaces of the front and back ends, so that both parties can work together efficiently.

10. Performance testing and optimization loop:

Perform regular performance testing and work with the backend team to identify and resolve performance issues. Optimization is an ongoing process that requires constant iteration and improvement.

11. Knowledge sharing and training:

Regular knowledge sharing meetings or trainings are held to enable front-end and back-end engineers to understand each other's work and technology, and to promote cooperation and collaboration.

Through the above methods, front-end engineers and back-end engineers can work together to optimize the overall performance and provide better user experience and application performance.

50. How do you deal with the balance between accessibility and performance optimization of front-end applications? Ever run into a conflict between performance optimization and accessibility?

The balance between dealing with accessibility issues of front-end applications and optimizing for performance is a key challenge as there can be conflicts between the two. However, it is crucial to ensure that the application performs well in terms of both performance and accessibility. Here are some ways to balance the two and avoid possible conflicts:

1. Prioritize accessibility:

Make accessibility a top priority and make sure your app is usable for all users, including those with disabilities. Accessibility should not be sacrificed for performance optimization.

2. Follow standards and best practices:

Use code and design patterns that comply with accessibility standards such as WCAG to ensure that your app is friendly to screen readers and other assistive technologies. These criteria often help improve performance.

3. Simplified page structure:

Simplify page structure and code, reducing unnecessary DOM elements and nesting, helping to improve performance and accessibility.

4. Test and Evaluation:

Conduct regular accessibility testing to ensure that your app performs well in terms of accessibility. This can help you identify and resolve potential conflict issues.

5. Use ARIA attributes:

Use ARIA attributes (Accessibility Roles and Attributes) to improve your app's performance with assistive technologies such as screen readers. However, care needs to be taken when using ARIA to avoid adverse effects on performance.

6. Lazy loading and chunked loading:

Use techniques like lazy loading and chunked loading to improve performance, but make sure these optimizations don't affect accessibility. Make sure core content remains accessible and usable.

7. Performance Testing:

When optimizing for performance, always perform performance testing to ensure that optimizations do not reduce accessibility. A balance between the two can be verified through regular testing.

8. Design and User Experience:

Bring design and user experience to the foreground by designing well-designed user interfaces and interactions to meet both performance and accessibility needs.

Although there may be some conflicts, in reality, performance optimization and accessibility are not necessarily mutually exclusive. Many performance optimization measures, such as simplifying page structure, compressing resources, reducing network requests, etc., can actually improve accessibility as well. It's important to maintain a balance and consider both aspects during design, development, and testing to ensure that your app provides a great experience in terms of both performance and accessibility.