• Declarative Rendering: Vue extends standard HTML with a template syntax that allows us to declaratively describe HTML output based on JavaScript state.

• Reactivity: Vue automatically tracks JavaScript state changes and efficiently updates the DOM when changes happen.

The object we are passing into createApp is in fact a component. Every app requires a "root component" that can contain other components as its children.

Instead of a computed property, we can define the same function as a method. For the end result, the two approaches are indeed exactly the same. However, the difference is that computed properties are cached based on their reactive dependencies. A computed property will only re-evaluate when some of its reactive dependencies have changed. This means as long as author.books has not changed, multiple access to publishedBooksMessage will immediately return the previously computed result without having to run the getter function again.

Vue uses an HTML-based template syntax that allows you to declaratively bind the rendered DOM to the underlying component instance's data. All Vue templates are syntactically valid HTML that can be parsed by spec-compliant browsers and HTML parsers.

Under the hood, Vue compiles the templates into highly-optimized JavaScript code. Combined with the reactivity system, Vue can intelligently figure out the minimal number of components to re-render and apply the minimal amount of DOM manipulations when the app state changes.

With Options API, we use the data option to declare reactive state of a component. The option value should be a function that returns an object. Vue will call the function when creating a new component instance, and wrap the returned object in its reactivity system. Any top-level properties of this object are proxied on the component instance (this in methods and lifecycle hooks).

A common need for data binding is manipulating an element's class list and inline styles. Since class and style are both attributes, we can use v-bind to assign them a string value dynamically, much like with other attributes. However, trying to generate those values using string concatenation can be annoying and error-prone. For this reason, Vue provides special enhancements when v-bind is used with class and style. In addition to strings, the expressions can also evaluate to objects or arrays.