Angular directives are fundamental building blocks of Angular applications, serving as the instructions to modify the DOM in response to specific conditions. They come in three types: component directives, which create reusable UI components; structural directives, like *ngFor and *ngIf, that change the structure of the DOM by adding or removing elements; and attribute directives, which apply behavior or modify the appearance of existing elements. Understanding how to use these directives effectively is crucial for creating dynamic web applications that respond to user interactions seamlessly.

When diving into Angular directives, beginners should focus on how to create and utilize their own custom directives. This involves defining a new directive using the @Directive decorator and specifying its behavior via the host and selector properties. By experimenting with directives, developers can learn to enhance the functionality of their applications while maintaining clean and manageable code. In summary, mastering Angular directives not only empowers developers to create sophisticated user interfaces but also streamlines the application development process.

When it comes to developing applications with Angular, performance optimization is crucial for providing users with a seamless experience. Here are 10 essential tips you can implement to boost your Angular app's performance. First, consider using OnPush change detection strategy to limit the number of checks the framework must perform. This can significantly reduce the workload on the application, especially in complex UIs. Secondly, leverage the Lazy Loading feature to load only the modules necessary for a specific route. By adopting lazy loading, you can decrease the initial loading time, making your application feel faster and more efficient.

Another key tip is to ensure you are using trackBy in your ngFor directives. This helps Angular to identify which items have changed, thus minimizing DOM manipulations. Additionally, utilize AOT (Ahead-of-Time) Compilation to pre-compile your templates during the build process, which can lead to faster rendering and fewer runtime errors. Consider optimizing your bundle size by removing unused modules and libraries, as smaller files lead to quicker load times. Lastly, use Performance Profiling tools available in the Angular framework to analyze and make data-driven decisions about improving your app's performance.

Building responsive web applications with Angular involves utilizing its powerful features like components, services, and modules to create a seamless user experience across different devices. First, ensure that you have a solid understanding of the Angular framework and its core concepts. You can achieve responsiveness by following these steps:

1. Use Angular's built-in responsive design functionalities to ensure your application adapts to various screen sizes.
2. Employ CSS frameworks like Bootstrap or Angular Material, which provide responsive grid systems and UI components.
3. Implement flexible layouts using CSS Flexbox or Grid to allow components to adjust dynamically.

Additionally, leverage Angular's media queries in your stylesheets to apply different styles based on the device's characteristics. This helps in tweaking UI elements for better accessibility and usability. To build a truly responsive application, consider the following practices:

• Optimize your images and resources for different screen resolutions.
• Utilize Angular's lazy loading feature to enhance performance by loading only the necessary modules at runtime.
• Conduct thorough testing across various devices and browsers to identify and fix responsiveness issues.