Optimizing a Slow Legacy Angular Application: A Step-by-Step Approach
As software developers, we often get a chance to work on existing legacy applications. These applications can be challenging, especially when previous developers have left behind a messy and tangled codebase. One of the most common and frustrating issues frontend developers face in these scenarios is slow rendering, which can significantly degrade the user experience and the application's overall performance.
Lets assume you run your Angular application and got to find the home page taking an agonizing 2–3 minutes to load. This not only frustrates users but also undermines the credibility and usability of your application. For many developers, the big question is, where do you start? The problem can seem overwhelming, and without a clear plan, it’s easy to get lost in the complexity of the legacy code.
This article aims to provide a structured approach to diagnosing and resolving performance issues in a legacy Angular application. We’ll walk you through essential steps, from the initial assessment to implementing advanced optimization techniques.
Step 1: Initial Assessment
Initial Assessment is a crucial step in optimizing a slow legacy Angular application. It helps in understanding the root causes of the performance issues and guides the subsequent optimization efforts. Here’s a detailed step by step process on how to effectively carry out the initial assessment.
Profiling the Application
- Angular DevTools:
Angular DevTools is a browser extension available for Chrome and Firefox. Install it from the respective web stores
Usage: Open your application in the browser, launch the Angular DevTools, and inspect the component tree. This tool provides insights into the change detection cycles, helping you identify components that are causing performance bottlenecks.
2. Chrome DevTools:
Performance Tab: Use the Performance tab to record the page load. Start recording before you reload the page and stop after the load completes. Analyze the recorded timeline to identify long tasks, scripting time, rendering time, and network activity.
Network Tab: Check the Network tab to see all the network requests made during the page load. Look for large payloads, long-loading resources, and requests that can be deferred or optimized.
3. Lighthouse:
Audit: Run a Lighthouse audit (available in Chrome DevTools under the “Lighthouse” tab). This provides a comprehensive report on various performance metrics like First Contentful Paint (FCP), Time to Interactive (TTI), and Total Blocking Time (TBT).
Lighthouse also provides actionable recommendations for improving performance, which can be extremely helpful in guiding your optimization efforts.
Identifying Bottlenecks
4. Initial Load Analysis:
Critical Rendering Path: Understand the critical rendering path, which includes everything that must happen to render the initial view. This includes HTML parsing, CSS parsing, JavaScript execution, and rendering.
Time to First Byte (TTFB): Measure the time taken to receive the first byte from the server. A high TTFB could indicate server-side performance issues.
5. Script Execution:
Main Thread Work: Analyze the main thread activities. Look for long-running tasks that block the main thread and prevent the page from becoming interactive.
JavaScript Parsing and Execution: Identify heavy JavaScript files and understand the time taken to parse and execute them. This can help pinpoint scripts that need optimization or deferment.
6. Rendering Performance:
Reflows and Repaints: Excessive reflows and repaints can significantly slow down rendering. Use tools to identify these issues and understand which parts of the DOM are causing them.
DOM Complexity: Analyze the complexity of the DOM. A very large DOM can slow down rendering and increase the time to interactive. Simplifying the DOM can lead to performance improvements.
Data Collection and Analysis
7. Data Logging:
Log Key Metrics: Log key performance metrics such as First Paint, First Contentful Paint, Largest Contentful Paint, and Time to Interactive. Use tools like Google Analytics to track these metrics over time.
Error Logging: Ensure that errors and warnings are logged and monitored. Tools like Sentry can help track runtime errors that may affect performance.
8. User Feedback:
Gather feedback from users regarding performance issues. Sometimes, real-world usage patterns can highlight performance problems that are not apparent during development and testing.
By conducting a thorough initial assessment, you can gather essential data and insights into the performance bottlenecks of your Angular application. This step lays the foundation for making informed decisions in the subsequent optimization process.
Step 2: Identify and Prioritize Issues
After conducting a thorough initial assessment, the next step is to identify and prioritize the performance issues affecting your Angular application. This step involves analyzing the collected data, pinpointing specific bottlenecks, and prioritizing them based on their impact on performance.
Network Analysis
- Examine Network Requests:
Payload Sizes: Identify large payloads that are being loaded during the initial page load. Look for opportunities to reduce the size of these payloads through compression or optimization.
Slow API Calls: Identify API calls that are taking a long time to complete. These calls may need optimization on the server side or could benefit from caching mechanisms.
Redundant Requests: Look for duplicate or redundant requests that can be eliminated to reduce network overhead.
2. Resource Prioritization:
Critical Resources: Identify critical resources that are essential for the initial render. Ensure that these resources are prioritized and loaded as early as possible.
Defer Non-Critical Resources: Defer loading of non-critical resources until after the initial render using techniques like `defer` and `async` attributes for scripts.
Code Analysis
3. Review Angular Code:
Large Components: Identify large and complex components that may be contributing to slow load times. Break these components into smaller, more manageable pieces.
Look for unused modules and services that can be removed to reduce the overall size of the application.
Identify inefficient or redundant code that can be optimized. Look for opportunities to refactor and improve code efficiency.
4. Check for Blocking Operations:
Synchronous Operations: Identify synchronous operations that are blocking the main thread. Consider making these operations asynchronous to improve performance.
Heavy Computations: Locate heavy computations that are happening during the initial load. Move these computations to web workers if possible, to avoid blocking the main thread.
Routing Analysis
5. Examine Angular Routing Configuration:
Eager vs. Lazy Loading: Check if all modules are being eagerly loaded or if lazy loading is being used effectively. Eager loading all modules can significantly slow down the initial load.
Route Splitting: Implement route splitting to load modules only when needed. Use the `loadChildren` syntax in the routing configuration to enable lazy loading.
const routes: Routes = [
{ path: 'feature', loadChildren: () => import('./feature/feature.module').then(m => m.FeatureModule) }
];Bundle Analysis
6. Use Webpack Bundle Analyzer:
Visualization: Use Webpack Bundle Analyzer to visualize the size of the output files and understand the composition of your bundles. This tool helps identify large bundles and the specific components or modules contributing to their size.
Identify Heavy Third-Party Libraries: Determine if any heavy third-party libraries are included in your bundles. These libraries may not be optimized for tree shaking and can significantly increase bundle size.
Optimize and Prioritize
7. Tree Shaking:
Ensure Tree Shaking is Enabled: Verify that tree shaking is enabled in your Angular build configuration to remove unused code from the bundles.
Move Heavy Libraries: Move heavy third-party libraries to separate modules and load them lazily if they are not needed for the initial load.
8. Code Splitting:
Implement Code Splitting: Break down large bundles using code splitting strategies. Ensure only necessary code is loaded initially by implementing route-based and component-based code splitting.
Dynamic Imports: Use dynamic imports for modules and components that are not immediately needed.
import('./path/to/module').then(m => m.SomeModule);Prioritize Issues
9. Impact Assessment:
Prioritize the identified issues based on their impact on performance. Focus on the issues that will have the most significant effect on reducing load times and improving user experience.
Identify quick wins that can be implemented easily and provide immediate performance improvements.
10. Create an Action Plan:
Create a roadmap for addressing the prioritized issues. Outline the steps needed to implement the optimizations and set realistic timelines for each task.
Collaborate with your team to ensure everyone is aligned on the priorities and the action plan. Assign tasks and responsibilities to team members.
By thoroughly identifying and prioritizing the performance issues in your Angular application, you can focus your efforts on the most impactful optimizations. This step ensures a targeted approach to improving performance and sets the stage for successful implementation in the subsequent steps.
Step 3: Optimize Network Requests
Optimizing network requests is crucial for improving the load time and overall performance of your Angular application. This step focuses on reducing the size and number of network requests, deferring non-critical resources, and optimizing API calls.
Reduce Payload Size
1. Compress Assets:
Gzip/Brotli Compression: Ensure that assets such as JavaScript, CSS, and HTML files are compressed using gzip or brotli. Configure your server to serve compressed versions of these files to reduce their size and improve load times.
2. Minify JavaScript and CSS:
Minification: Use Angular CLI to build production bundles with minification enabled. Minification reduces the size of JavaScript and CSS files by removing whitespace, comments, and unnecessary characters.
Build Configuration: Ensure that your `angular.json` configuration includes optimization settings for production builds.
"configurations": {
"production": {
"optimization": true,
"outputHashing": "all",
"sourceMap": false,
"extractCss": true,
"namedChunks": false,
"aot": true,
"extractLicenses": true,
"vendorChunk": false,
"buildOptimizer": true
}
}3. Reduce Image Sizes:
Optimize Images: Use modern image formats like WebP, which offer better compression and quality. Ensure images are properly sized and compressed.
Lazy Loading Images: Implement lazy loading for images using the `loading=”lazy”` attribute to defer loading of off-screen images.
<img src="path/to/image.webp" loading="lazy" alt="Description">Implement Lazy Loading
4. Lazy Loading Angular Modules:
LoadChildren Syntax: Use the `loadChildren` syntax in the routing configuration to implement lazy loading for non-critical modules. This ensures that only the necessary code for the initial load is fetched, deferring the loading of other modules until they are needed.
const routes: Routes = [
{ path: 'feature', loadChildren: () => import('./feature/feature.module').then(m => m.FeatureModule) }
];5. Lazy Load Components:
Dynamic Imports: Use dynamic imports to lazy load components that are not required immediately. This helps reduce the initial bundle size and improve load times.
import('./path/to/component').then(m => m.SomeComponent);Optimize API Calls
6. Reduce API Payload Sizes:
Optimize Responses: Ensure that API responses contain only the necessary data. Avoid sending large payloads or unnecessary fields that are not required by the client.
Pagination and Filtering: Implement pagination and filtering on the server side to limit the amount of data sent in each response.
7. Combine Multiple API Calls:
Batch Requests: Combine multiple API calls into a single request where possible. This reduces the number of network round trips and improves overall performance.
GraphQL: Consider using GraphQL if your application makes multiple related API calls. GraphQL allows you to fetch all the required data in a single request, reducing network overhead.
8. Caching API Responses:
Client-Side Caching: Use browser caching strategies to cache API responses on the client side. Implement HTTP caching headers such as `Cache-Control` and `ETag` to enable efficient caching.
Service Worker: If your application is a Progressive Web App (PWA), leverage the Angular Service Worker to cache API responses and assets.
Defer Non-Critical Resources
9. Async and Defer Attributes:
Load Scripts Asynchronously: Use the `async` and `defer` attributes for non-critical scripts to load them asynchronously or defer their execution until after the initial page load.
<script src="path/to/script.js" async></script>
<script src="path/to/script.js" defer></script>10. Preload Critical Resources:
Resource Hints: Use resource hints like `<link rel=”preload”>` and `<link rel=”prefetch”>` to preload critical resources and prefetch resources that might be needed soon.
<link rel="preload" href="path/to/critical-resource.js" as="script">
<link rel="prefetch" href="path/to/non-critical-resource.js">Evaluate and Monitor
11. Continuous Monitoring:
Track Network Performance: Use tools like Google Analytics, Sentry, or New Relic to monitor network performance and identify slow or problematic requests in real-time.
Adjust and Optimize: Continuously adjust and optimize network requests based on monitoring data and performance metrics.
12. Performance Testing:
Regular Audits: Conduct regular performance audits using tools like Lighthouse and WebPageTest to ensure that network optimizations are effective and that there are no regressions.
By optimizing network requests, you can significantly improve the load time and performance of your Angular application. This step focuses on reducing the size and number of requests, deferring non-critical resources, and ensuring that API calls are efficient and effective.
Step 4: Analyze and Optimize Bundles
Optimizing bundles is essential to reduce the load time and improve the performance of your Angular application. This step involves using tools to analyze the bundle size, implementing tree shaking, and applying code splitting strategies to ensure that only the necessary code is loaded initially.
Analyze Bundles
1. Webpack Bundle Analyzer:
Installation: Install Webpack Bundle Analyzer using npm.
Configuration: Configure Webpack Bundle Analyzer in your Angular project to visualize the size of the output files and understand the composition of your bundles.
npm install - save-dev webpack-bundle-analyzer- In your `angular.json` file, modify the build configuration to include the analyzer:
"configurations": {
"production": {
"plugins": [
{
"name": "webpack-bundle-analyzer",
"options": {
"analyzerMode": "static",
"reportFilename": "bundle-report.html"
}
]
}
}Usage: Run the build command to generate the bundle report.
ng build - prodOpen the `bundle-report.html` file to visualize the bundle size and composition.
2. Identify Large Bundles:
Component and Module Size: Identify large components and modules contributing to the bundle size. Focus on optimizing these first to achieve significant improvements.
Implement Tree Shaking
3. Enable Tree Shaking:
Angular CLI Configuration: Ensure tree shaking is enabled in your Angular build configuration. Tree shaking removes unused code from the final bundle.
"configurations": {
"production": {
"optimization": true,
…
}
}4. Optimize Third-Party Libraries:
Import Specific Modules: When using third-party libraries, import only the specific modules you need instead of the entire library. This reduces the bundle size by including only the necessary code.
// Instead of importing the whole library
import * as _ from 'lodash';
// Import only the specific functions you need
import { map, filter } from 'lodash';Implement Code Splitting
5. Route-Based Code Splitting:
Lazy Loading Modules: Use Angular’s lazy loading feature to split your code at the route level. This ensures that only the necessary modules are loaded initially, deferring the rest until they are needed.
const routes: Routes = [
{ path: 'feature', loadChildren: () => import('./feature/feature.module').then(m => m.FeatureModule) }
];6. Component-Based Code Splitting:
Dynamic Imports: Use dynamic imports to lazy load components that are not required immediately. This helps reduce the initial bundle size.
import('./path/to/component').then(m => m.SomeComponent);7. Optimize Angular Material:
Specific Imports: If using Angular Material, import individual components rather than the entire library to reduce the bundle size.
import { MatButtonModule } from '@angular/material/button';
import { MatInputModule } from '@angular/material/input';Evaluate and Monitor
8. Continuous Monitoring:
Track Bundle Size: Continuously monitor the size of your bundles using Webpack Bundle Analyzer or similar tools. Identify and address any regressions that increase the bundle size.
Performance Testing: Regularly test the performance of your application using tools like Lighthouse and WebPageTest to ensure that the optimizations are effective.
9. Adjust and Optimize:
Refactor Code: Based on the analysis, refactor the code to further reduce the bundle size. Remove any unnecessary dependencies and optimize the code structure.
Documentation: Document the changes made and best practices followed to ensure that future code additions do not negatively impact the bundle size.
By analyzing and optimizing bundles, you can significantly improve the load time and performance of your Angular application. This step ensures that only the necessary code is loaded initially, reducing the overall size of the bundles and enhancing the user experience.
Step 5: Enhance Rendering Performance
Improving the rendering performance of your Angular application is crucial for providing a smooth and responsive user experience. This step involves optimizing how the application handles DOM updates, reducing reflows and repaints, and implementing efficient change detection strategies.
Reduce Reflows and Repaints
- Minimize Direct DOM Manipulations:
Angular Directives: Use Angular’s built-in structural directives like `*ngIf` and `*ngFor` to control the rendering of elements efficiently. Avoid direct DOM manipulations in your components.
<div *ngIf="condition">Content goes here</div>2. Optimize CSS:
Avoid Complex Selectors: Use simple and efficient CSS selectors to reduce the impact on rendering performance. Complex selectors can slow down the rendering process.
Batch Style Changes: Group style changes together to minimize reflows. Making multiple individual style changes can trigger multiple reflows and repaints.
Optimize Change Detection
3. Use OnPush Change Detection:
ChangeDetectionStrategy.OnPush: Apply the `OnPush` change detection strategy for components that do not frequently change. This reduces the frequency of change detection cycles and improves performance.
import { ChangeDetectionStrategy, Component } from '@angular/core';
@Component({
selector: 'app-optimized-component',
templateUrl: './optimized-component.component.html',
changeDetection: ChangeDetectionStrategy.OnPush
})
export class OptimizedComponent {
// Component logic here
}4. Immutable Data Structures:
Immutable Objects: Use immutable data structures and immutability patterns to ensure that change detection is triggered only when necessary. Immutable data makes it easier to track changes and optimize performance.
Implement Efficient Rendering Techniques
5. Virtual Scrolling:
Angular CDK Virtual Scroll: Implement virtual scrolling for large lists or tables using Angular CDK’s `cdk-virtual-scroll-viewport`. This technique renders only the visible items, significantly improving performance for large datasets.
<cdk-virtual-scroll-viewport itemSize="50" class="viewport">
<div *cdkVirtualFor="let item of items" class="item">{{ item }}</div>
</cdk-virtual-scroll-viewport>6. TrackBy in NgFor:
TrackBy Function: Use the `trackBy` function with `*ngFor` to improve the performance of list rendering. This helps Angular track which items have changed, added, or removed, reducing the number of DOM manipulations.
<div *ngFor="let item of items; trackBy: trackByFn">{{ item.name }}</div>trackByFn(index, item) {
return item.id; // or unique identifier
}Optimize Image Loading
7. Lazy Load Images:
Lazy Loading: Implement lazy loading for images using the `loading=”lazy”` attribute. This defers the loading of images until they are in the viewport, improving the initial load time.
<img src="path/to/image.webp" loading="lazy" alt="Description">8. Optimize Image Sizes:
Responsive Images: Use responsive images to serve appropriately sized images based on the device’s screen size. This reduces the amount of data transferred and improves rendering performance.
<img srcset="small.jpg 500w, medium.jpg 1000w, large.jpg 2000w" sizes="(max-width: 600px) 480px, 800px" src="medium.jpg" alt="Description">Implement Caching Strategies
9. Client-Side Caching:
Browser Cache: Leverage browser caching strategies to cache static assets like CSS, JavaScript, and images. Use HTTP caching headers like `Cache-Control` and `ETag` to improve load times.
10. Service Worker:
Angular Service Worker: If your application is a Progressive Web App (PWA), use the Angular Service Worker to cache assets and API responses. This allows the application to load faster and function offline.
ng add @angular/pwaBy enhancing the rendering performance of your Angular application, you can create a more responsive and smooth user experience. This step involves optimizing how the application handles DOM updates, reducing unnecessary reflows and repaints, and implementing efficient change detection and rendering techniques.
Step 6: Implement Monitoring and Continuous Improvement
To ensure sustained performance and quickly identify any regressions or new issues, it’s essential to set up monitoring and adopt a continuous improvement approach. This step involves implementing performance monitoring tools, establishing performance benchmarks, and regularly reviewing and optimizing your application’s performance.
Set Up Monitoring Tools
1. Google Analytics:
Page Load Metrics: Use Google Analytics to track page load times and other key performance metrics. Set up custom reports to monitor performance over time.
2. Performance Monitoring Services:
New Relic, Dynatrace, or Sentry: Integrate these tools to monitor real-time performance, error rates, and user experience. These services provide detailed insights into application performance and help identify bottlenecks.
3. Lighthouse CI:
Automated Performance Audits: Integrate Lighthouse CI into your CI/CD pipeline to perform automated performance audits. This helps maintain performance standards and detect regressions early.
Establish Performance Benchmarks
4. Define Metrics:
Key Performance Indicators (KPIs): Define KPIs such as First Contentful Paint (FCP), Time to Interactive (TTI), Largest Contentful Paint (LCP), and Cumulative Layout Shift (CLS). These metrics provide a comprehensive view of the application’s performance.
5. Baseline Performance:
Initial Benchmarks: Conduct initial performance tests to establish baseline metrics. Use tools like Lighthouse, WebPageTest, or PageSpeed Insights to gather these metrics.
Continuous Review and Optimization
6. Regular Performance Audits:
Scheduled Audits: Perform regular performance audits to identify new bottlenecks and areas for improvement. Use the data from monitoring tools to guide these audits.
7. Iterative Improvements:
Performance Sprints: Allocate dedicated time for performance improvements in your development sprints. Focus on addressing the most significant issues identified in audits and monitoring reports.
8. User Feedback:
Collect Feedback: Gather feedback from users regarding performance issues. User feedback can provide valuable insights into real-world performance and highlight areas that need attention.
Best Practices and Documentation
9. Document Performance Best Practices:
Guidelines: Create and maintain documentation outlining performance best practices for your team. Include guidelines for writing efficient code, optimizing assets, and using Angular features effectively.
10. Training and Awareness:
Regularly train your development team on performance optimization techniques and tools. Ensure that performance considerations are integrated into the development process.
Proactive Monitoring and Alerts
11. Set Up Alerts:
Performance Thresholds: Configure alerts in your monitoring tools to notify you when performance metrics exceed predefined thresholds. This allows for quick response to potential issues.
12. Performance Dashboards:
Real-Time Dashboards: Create real-time performance dashboards to provide an at-a-glance view of the application’s health. This helps in quickly identifying and addressing performance problems.
By implementing monitoring and continuous improvement practices, you can ensure that your Angular application’s performance remains optimal over time. This step involves setting up comprehensive monitoring tools, establishing benchmarks, conducting regular audits, and fostering a culture of performance awareness and iterative optimization.
Optimizing a legacy Angular application might seem challenging, but breaking it down into manageable steps can make it an exciting and rewarding process. Start with a thorough initial assessment to understand the current performance issues. Next, optimize your routing and network requests to ensure faster load times and efficient resource use. Tools like Webpack Bundle Analyzer can help you implement lazy loading and reduce bundle sizes.
Enhance your code efficiency and improve rendering to create a smoother, faster user experience. Remember, continuous monitoring is key to maintaining performance as your application grows.
By following these steps, you can turn a slow, outdated Angular app into a high-performing, efficient one. This not only boosts user satisfaction but also prepares your app for future growth. Keep testing, monitoring, and refining your code to stay ahead. With a bit of diligence and a proactive approach, performance optimization can become a fulfilling part of your development journey.
