Performance degradation after migration to Angular

After migrating from AngularJS to Angular, it is common to experience performance degradation. This can happen due to several reasons that are either a result of improper migration strategies or inherent differences in the architecture of AngularJS and Angular. Below are the most common causes of performance issues and how to troubleshoot them:

1. Inefficient Use of ngUpgrade

The ngUpgrade module allows AngularJS and Angular to work together, but this introduces a performance overhead because it enables two different frameworks to run simultaneously. Here’s how it can affect performance:

• Hybrid App Performance: When AngularJS and Angular components coexist in the same app, the browser has to manage both change detection cycles, increasing the complexity and potentially leading to slower rendering times.

Solution:

• Gradually transition more functionality to Angular by ensuring the AngularJS components are progressively migrated to Angular.
• Avoid keeping large sections of the app in the hybrid mode for too long. Focus on completely migrating individual modules or features.

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2. Inefficient Change Detection

Angular’s change detection strategy is more powerful and flexible than AngularJS’s, but it can also introduce performance issues if not used correctly:

• Default Change Detection: In Angular, the default change detection checks all components on every event, leading to unnecessary updates.
• ngUpgrade and Digest Cycle: Since AngularJS still uses its $digest cycle for change detection, this could conflict with Angular’s change detection, causing performance degradation due to redundant checks.

Solution:

• Use OnPush Change Detection: Switch Angular components to OnPush change detection wherever possible. This tells Angular to only check for changes when inputs change, significantly reducing the number of checks. @Component({ selector: 'app-my-component', changeDetection: ChangeDetectionStrategy.OnPush, templateUrl: './my-component.component.html', })
• Optimize $digest Cycle in AngularJS: You can also optimize the $digest cycle in AngularJS by minimizing the number of watchers or using $scope.$applyAsync to batch updates.

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3. Component Downgrading Issues

When downgrading Angular components to be used in AngularJS, if not done properly, it can cause performance issues:

• Angular Component in AngularJS: Downgraded Angular components may still rely on AngularJS’s $scope and $rootScope, leading to unnecessary watchers or repeated digest cycles when interacting with AngularJS data.

Solution:

• Make sure the downgraded Angular components are as efficient as possible.
• Use Angular’s ngUpgrade module carefully. Downgrade components only when needed and try to minimize the number of Angular components being used in the AngularJS side.

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4. Inefficient $watch Usage in AngularJS

One of the primary reasons for slow performance in AngularJS applications is excessive $watch usage. With $watch, AngularJS keeps track of changes to the scope and runs a comparison (digest cycle) to update the DOM.

• Too many $watch calls: If there are too many $watch expressions or complex expressions being evaluated frequently, it can severely degrade performance.

Solution:

• Minimize $watch Usage: Try to reduce the number of $watch expressions or make them more specific by limiting the scope of what is being watched.
• Use $watchCollection for Arrays: When watching arrays or objects, $watchCollection can be more efficient than $watch since it only triggers a digest cycle when the array’s structure changes.
• Use ngModelOptions with Debouncing: For forms or inputs bound with ngModel, use debouncing to limit the frequency of change detection updates.

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5. Unnecessary Dependencies in AngularJS Components

During the migration process, some AngularJS components may still depend on AngularJS-specific services or APIs. These dependencies can affect performance due to their need to interact with AngularJS and Angular, causing unnecessary complexity.

Solution:

• Gradually Migrate Services: Start by upgrading services from AngularJS to Angular so that AngularJS components rely less on AngularJS-specific services.
• Avoid Using $http and $resource: When transitioning to Angular, replace AngularJS’s $http and $resource with Angular’s HttpClient. Continuing to use $http can create performance overhead.

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6. Hybrid Routing and Navigation Performance Issues

In a hybrid AngularJS and Angular application, routing can be complex, and improper configuration can lead to performance degradation:

• AngularJS and Angular Routing Conflict: Both AngularJS and Angular use their own routers, and improper configuration may cause navigation issues or delays during routing transitions.

Solution:

• Use ui-router for AngularJS and Angular Router for Angular, and use ngUpgrade’s upgradeRouter to handle routing between the two frameworks.
• Gradually migrate routes to Angular Router to eliminate the need for hybrid routing.

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7. Legacy Code and Event Listeners

After migrating to Angular, your application might still contain legacy code or event listeners that are no longer needed in Angular. These can cause memory leaks or slow down your application.

Solution:

• Remove Unused Event Listeners: Ensure that all event listeners that were set up in AngularJS are properly removed when they’re no longer required.
• Use Angular’s Renderer2 for Event Binding: Instead of using AngularJS’s event system, adopt Angular’s Renderer2 to attach and remove event listeners to prevent memory leaks.

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8. Excessive DOM Manipulation in Hybrid Apps

One of the biggest performance concerns when working with a hybrid AngularJS and Angular app is DOM manipulation. Angular uses a more optimized approach to manipulating the DOM, whereas AngularJS can be less efficient due to its older digest cycle mechanism.

Solution:

• Avoid Direct DOM Manipulation: Ensure that DOM manipulations in AngularJS components are kept to a minimum. Rely on Angular’s declarative templates for efficient DOM updates.
• Transition to Angular Components: As you migrate, try to use Angular components for UI rendering instead of mixing AngularJS directives and components in the same view.

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9. Performance Monitoring and Optimization

When working with a hybrid application, it’s essential to monitor and optimize performance continuously. Angular and AngularJS apps have different performance profiles, and when running together, issues may arise.

Solution:

• Use Performance Tools: Leverage browser tools like Chrome DevTools, Angular Profiler, and ngUpgrade Debugging to identify bottlenecks and performance issues.
• Lazy Load Modules: In Angular, take advantage of lazy loading to load features only when necessary.
• Track Memory Usage: Use Angular’s built-in tools to track memory consumption and avoid memory leaks.

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10. Caching Issues and Service Workers

Some hybrid apps might face performance degradation due to improper caching or service workers not being set up correctly.

Solution:

• Use Service Workers for Caching: Implement service workers for caching your app’s assets and API calls to reduce load times.
• Cache API Responses: Use caching strategies for API responses to avoid redundant network calls, which can improve performance after migration.