Vue.js is a progressive JavaScript framework used for building user interfaces and single-page applications. Its core concepts revolve around three main elements: the Vue instance, the template system, and reactivity. The Vue instance acts as the root of every Vue application and is crafted by invoking the new Vue() constructor. This instance controls the application’s data and enables the implementation of features like data binding and event handling. Understanding these basic components is crucial for any beginner looking to harness the power of Vue.js.

At the heart of Vue.js is its reactive data binding which allows the framework to automatically update the DOM whenever the underlying data changes. This means that developers can work more efficiently, as Vue.js takes care of syncing the view with the model without the need for direct DOM manipulation. In conjunction with the template syntax, which embraces a declarative approach to rendering the UI, these features simplify the development process and enhance productivity. As you delve deeper, you'll discover additional concepts such as components and directives that further extend the capabilities of Vue.js.

Vue.js is a progressive JavaScript framework that has gained immense popularity among developers for building user interfaces and single-page applications. One of its most attractive aspects is its versatility. Thanks to its component-based architecture, developers can break down complex applications into smaller, manageable components. This modular structure allows for rapid development and easier maintenance, making it essential for both new and experienced developers to get acquainted with.

Here are 10 essential Vue.js features every developer should know:

1. Reactive Data Binding: Vue's reactivity system automatically updates the view whenever the model changes.
2. Computed Properties: These are cached properties that depend on reactive data, enhancing performance.
3. Directives: Vue’s built-in directives like v-bind and v-model simplify DOM manipulations.
4. Vue Router: This allows developers to create a single-page application with navigation.
5. Vuex: A state management pattern and library that helps manage the state of the application.
6. Custom Directives: Developers can create their own directives for customized behavior.
7. Transitions: Vue provides built-in transition effects for elements entering and leaving the DOM.
8. Scoped Slots: This feature allows for more flexible component designs through slot usage.
9. Vue CLI: A powerful command-line tool that efficiently scaffolds new projects.
10. Single File Components: Vue components can encapsulate HTML, JavaScript, and CSS in a single file, promoting better organization.

Building a robust application with Vue.js requires a solid understanding of its core principles and best practices. To start, ensure that your project is well-structured by organizing components wisely. Utilize single-file components to encapsulate templates, scripts, and styles, making your code easier to manage and more intuitive. Consider implementing a Vuex store for state management, which simplifies data flow across your application. Furthermore, leverage Vue Router for seamless navigation and maintainability of your app, allowing you to create a single-page application (SPA) experience effortlessly.

In addition to structural considerations, performance optimization is key in developing a robust Vue.js application. Always strive to keep your components lightweight and efficient by using the v-once directive on static content to reduce re-renders. Avoid using deep watchers where possible, as they can lead to performance bottlenecks. Implement code-splitting and lazy-loading techniques to ensure that only necessary components are loaded with the initial application, enhancing load times. Finally, regularly conduct unit tests and utilize tools like Vue Devtools to monitor performance, track state, and debug issues effectively.