Mastering Vue lifecycle is crucial for building robust applications. The Composition API has revolutionized component development by providing a more modular architecture. Traditional Vue lifecycle consists of eight phases, but with the Composition API, these methods can be broken down into smaller functions called hooks. Essential libraries and frameworks include Vue Router, Vuex, Pinia, Vee-Validate, and Vue Server Render.

Vue Watch is a feature that monitors changes to application state and updates components accordingly. With the release of Vue 3 and the Composition API, watchers have undergone significant transformation. The Composition API introduces "composables," reusable functions that can be used to create and manage watchers using the `watch` function. This approach improves code reusability, eases debugging, and enhances performance by reducing unnecessary re-renders.

**TL;DR Vue Computed properties allow reactive data that depends on other sources, running a function whenever a dependency changes to return a new value. They enable automatic re-rendering of components when data changes, encapsulate complex logic, and improve readability. The Composition API provides an elegant solution for managing dependencies with computed properties. Here's how to use them: Create a count ref and use the computed function to create a doubleCount property that is recalculated whenever count changes. Manage multiple dependencies using the computed function, such as fullName depending on both name and age. Prevent unnecessary recalculations with the memoize function in complex applications.

Guide compares Vue’s Options API and Composition API for organizing component logic, noting the Options API’s simplicity and suitability for small/legacy components, and the Composition API’s modularity, reusability, and testability for complex apps; advocates choosing per component, even mixing both, illustrated via a task management system workflow.

Article compares Vue’s Options API and Composition API for organizing component logic: Options is familiar and simple for small or legacy Vue 2 apps but can cause tight coupling and unwieldy components as complexity grows; Composition (Vue 3) brings functional patterns, loose coupling, better organization, reusability, and easier testing—ideal for large, scalable projects, illustrated by refactoring a reusable modal; choose based on needs.