What is the 'critical rendering path' and how can you optimize it?
Jun 28, 2025 am 01:25 AM
Optimizing key rendering paths can improve web page loading speed and user experience, and its core is to understand and optimize the entire process from code to pixels. First, the key steps include HTML parsing to generate DOM trees, CSS parsing to generate CSSOM, JavaScript execution, layout, drawing and synthesis. Delaying any step will cause page blank; second, optimization solutions include: compressing CSS and JS files, delaying non-essential JS, inline the key CSS on the first screen, and using async/defer attributes; second, priority is given to loading the first screen content, delaying non-element resources, and avoiding unnecessary frameworks; finally, key indicators such as FCP and TTI are measured and improved through tools such as Lighthouse and PageSpeed ??Insights, and continuously optimize the real user experience.
The critical rendering path is the sequence of steps a browser takes to turn HTML, CSS, and JavaScript into pixels on the screen. It's important because it directly affects page load speed and perceived performance. Optimizing it can make your site feel faster and more responsive.
Understand the Key Components
The critical rendering path includes several main parts: HTML parsing, CSSOM construction, JavaScript execution, layout (or reflow), painting, and compasing. Each step impacts how quickly content appears on the screen.
- HTML parsing builds the DOM tree.
- CSSOM construction turns styles into a structure the browser can understand.
- When JavaScript runs, it can block or modify both the DOM and CSSOM.
- Layout calculates where elements go on the page.
- Painting fills in pixels for each visible element.
- Compositing layers everything together for display.
If any of these steps are slow or blocked, users see a blank screen longer than necessary.
Optimize Render-Blocking Resources
Most performance issues come from render-blocking resources — especially JavaScript and CSS. The browser can't render the page until those files are processed.
Here's what you can do:
- Minify CSS and JavaScript : Smaller files mean less time downloading and parsing.
- Defer non-critical JavaScript : Load only what's needed for the initial view first.
- Inline critical CSS : Put the essential styles needed for above-the-fold content directly in the
. - Use
asyncordeferattributes : This tells the browser not to block HTML parsing when loading scripts.
For example, if you have an analytics script that doesn't affect page rendering, mark it as defer so it loads after the main content.
Prioritize Above-the-Fold Content
Above-the-fold content is what users see first without scrolling. If this part loads slowly, users perceive your site as slow overall.
To prioritize it:
- Load key HTML, CSS, and JS for that area first.
- Lazy-load images and videos below the fold.
- Avoid large JavaScript frameworks unless they're absolutely necessary.
You don't need to load the full page to show the headline and navigation bar. Doing this well can give users something to look at while the rest of the page finishes loading.
Use Tools to Measure and Improve
It's hard to optimize what you can't measure. Tools like Lighthouse , PageSpeed ??Insights , and browser DevTools help you see where the bottlenecks are.
They'll show things like:
- How long it takes to generate the first paint.
- Long tasks blocking the main thread.
- Unused JavaScript or CSS.
Run Lighthouse regularly and focus on improving the metrics it reports, like First Contentful Paint (FCP) and Time to Interactive (TTI). These numbers reflect real user experience.
Basically that's it. Optimizing the critical rendering path isn't overly complex, but it does require attention to detail and knowing which resources are truly critical.
The above is the detailed content of What is the 'critical rendering path' and how can you optimize it?. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Performance optimization and horizontal expansion technology of Go framework?
Jun 03, 2024 pm 07:27 PM
In order to improve the performance of Go applications, we can take the following optimization measures: Caching: Use caching to reduce the number of accesses to the underlying storage and improve performance. Concurrency: Use goroutines and channels to execute lengthy tasks in parallel. Memory Management: Manually manage memory (using the unsafe package) to further optimize performance. To scale out an application we can implement the following techniques: Horizontal Scaling (Horizontal Scaling): Deploying application instances on multiple servers or nodes. Load balancing: Use a load balancer to distribute requests to multiple application instances. Data sharding: Distribute large data sets across multiple databases or storage nodes to improve query performance and scalability.
Nginx Performance Tuning: Optimizing for Speed and Low Latency
Apr 05, 2025 am 12:08 AM
Nginx performance tuning can be achieved by adjusting the number of worker processes, connection pool size, enabling Gzip compression and HTTP/2 protocols, and using cache and load balancing. 1. Adjust the number of worker processes and connection pool size: worker_processesauto; events{worker_connections1024;}. 2. Enable Gzip compression and HTTP/2 protocol: http{gzipon;server{listen443sslhttp2;}}. 3. Use cache optimization: http{proxy_cache_path/path/to/cachelevels=1:2k
Apache Performance Tuning: Optimizing Speed & Efficiency
Apr 04, 2025 am 12:11 AM
Methods to improve Apache performance include: 1. Adjust KeepAlive settings, 2. Optimize multi-process/thread parameters, 3. Use mod_deflate for compression, 4. Implement cache and load balancing, 5. Optimize logging. Through these strategies, the response speed and concurrent processing capabilities of Apache servers can be significantly improved.
Performance optimization in Java microservice architecture
Jun 04, 2024 pm 12:43 PM
Performance optimization for Java microservices architecture includes the following techniques: Use JVM tuning tools to identify and adjust performance bottlenecks. Optimize the garbage collector and select and configure a GC strategy that matches your application's needs. Use a caching service such as Memcached or Redis to improve response times and reduce database load. Employ asynchronous programming to improve concurrency and responsiveness. Split microservices, breaking large monolithic applications into smaller services to improve scalability and performance.
PHP framework performance optimization: Exploration combined with cloud native architecture
Jun 04, 2024 pm 04:11 PM
PHP Framework Performance Optimization: Embracing Cloud-Native Architecture In today’s fast-paced digital world, application performance is crucial. For applications built using PHP frameworks, optimizing performance to provide a seamless user experience is crucial. This article will explore strategies to optimize PHP framework performance by combining cloud-native architecture. Advantages of Cloud Native Architecture Cloud native architecture provides some advantages that can significantly improve the performance of PHP framework applications: Scalability: Cloud native applications can be easily scaled to meet changing load requirements, ensuring that peak periods do not occur bottleneck. Elasticity: The inherent elasticity of cloud services allows applications to recover quickly from failures and maintain availability and responsiveness. Agility: Cloud-native architecture supports continuous integration and continuous delivery
How to consider performance optimization in C++ class design?
Jun 05, 2024 pm 12:28 PM
Tips for improving performance in C++ class design include: avoiding unnecessary copies, optimizing data layout, and using constexpr. Practical case: Use object pool to optimize object creation and destruction.
Scaling XML/RSS Processing: Performance Optimization Techniques
Apr 27, 2025 am 12:28 AM
When processing XML and RSS data, you can optimize performance through the following steps: 1) Use efficient parsers such as lxml to improve parsing speed; 2) Use SAX parsers to reduce memory usage; 3) Use XPath expressions to improve data extraction efficiency; 4) implement multi-process parallel processing to improve processing speed.
How to integrate performance optimization tools in Golang technology performance optimization?
Jun 04, 2024 am 10:22 AM
Integrating performance optimization tools into Golang technology performance optimization In Golang applications, performance optimization is crucial, and the efficiency of this process can be greatly improved with the help of performance optimization tools. This article will guide you through the step-by-step integration of popular performance optimization tools to help you conduct comprehensive performance analysis and optimization of your application. 1. Choose performance optimization tools. There are many performance optimization tools to choose from, such as: [pprof](https://github.com/google/pprof): a toolkit developed by Google for analyzing CPU and memory utilization. [go-torch](https://github.com/uber/go-torch):
