Optimising Angular.js: Performance Best Practices & Tools

Angular.js, an open-source, high-performance, and lightweight JavaScript platform developed by Google, is one of the primary technologies transforming the development of interactive and engaging single-page applications (SPAs). However, as applications intensify, performance may become a significant concern. Optimizing Angular.js is crucial for maintaining a positive user experience and ensuring the proper functioning of the application. This article discusses how to get the best out of Angular.js applications and offers some of the best tools to achieve this effectively.

Efficient Data Binding

Angular. js employs two-way data binding, but this makes development easier only if one does not take top performance into consideration. To optimise, prefer one-way data binding ({{:Some of the nodes ({{{link|data_access::read}}}) which may be offline and used only for read data access. This in turn reduces the number of watchers for Angular. It means that js needs to track, thus enhancing performance.

Limit Watchers

Angular.js relies on watchers to monitor changes in the scope, but too many watchers can slow down the application. Use tools like Batarang, a Chrome extension, to inspect and manage watchers. Optimize your code to minimize the number of watchers by:

• Using Angular’s track by clause in ng-repeat to track items by a unique identifier instead of object reference.
• Avoiding deep watching of complex objects unless absolutely necessary.
• Utilizing the ng-model-options directive to debounce model updates.

Asynchronous Operations

Leveraging Angular.js’s asynchronous operations can greatly enhance performance. Use $timeout and $interval sparingly and only when necessary. For HTTP requests, use $http or $resource services, and always handle responses asynchronously. This non-blocking approach helps in maintaining a responsive UI.

Use of ng-if and ng-show/ng-hide

The ng-if directive ensures elements are added or removed from the DOM based on conditions, leading to better performance compared to ng-show or ng-hide, which simply toggle CSS properties. Use ng-if for conditional rendering to minimize the DOM size and reduce processing overhead.

Minimize DOM Manipulation

Excessive DOM manipulation can degrade performance. Use Angular.js’s built-in directives for DOM manipulation instead of jQuery. When necessary, encapsulate DOM manipulation in directives, ensuring Angular.js is aware of the changes and can manage them efficiently.

Lazy Loading

Lazy loading modules and components can significantly enhance performance, especially for large applications. Use the ocLazyLoad module to load JavaScript files on demand. This reduces the initial load time and improves application responsiveness.

Optimise Filters and Expressions

Filters and expressions can become performance bottlenecks if overused or used improperly. Limit the use of filters in templates and prefer using them in controllers or services. Additionally, cache the results of complex expressions to avoid unnecessary recalculations.

Caching

Caching is a powerful technique to improve performance. Use $cacheFactory to create caches for HTTP responses and other data that doesn’t change frequently. This reduces the need for repeated data fetching and processing.

Reduce Digest Cycle Impact

The digest cycle is central to Angular.js’s change detection mechanism. Minimize the impact on the digest cycle by reducing the number of bindings and watchers, debouncing events, and avoiding heavy computations within the cycle. Use the $evalAsync method to defer expressions to the next digest cycle.

Tools for Performance Monitoring

Several tools can help monitor and optimize Angular.js performance:

• Batarang: A Chrome extension for debugging and profiling Angular.js applications.
• ng-stats: A tool that displays the number of watchers and scope count in real-time.
• Augury: A Chrome and Firefox extension for visualizing and debugging Angular applications.