The internal working principle of the effect function

Vue 3's `effect` function is the core of the reactive system, responsible for creating reactive side effects. When dependent data changes, it automatically re-executes. Internally, it maintains key data structures such as `activeEffect`, `effectStack`, and `targetMap`. When an effect is created, it instantiates a `ReactiveEffect` and immediately executes the `run` method. Dependency tracking is established through the `track` function, forming a three-level mapping relationship stored in a `WeakMap`. When data changes, the `trigger` function locates and executes the relevant effects. Effects support nested calls, with parent-child relationships managed via `effectStack`. A scheduler mechanism allows custom execution logic, and the returned `runner` can stop the effect. Internally, multiple optimizations are implemented, such as avoiding duplicate collection and cleaning up old dependencies. Both `computed` and `watch` are built on top of `effect`, handling various edge cases like self-increment loops and array methods. Debugging hooks are provided. Component rendering is essentially an effect, collaborating with the scheduler to achieve efficient updates.

The detailed process of dependency collection and tracking

The core of Vue 3's reactivity system is dependency collection and tracking, achieved by intercepting get/set operations through Proxy, combined with the `track` and `trigger` functions to automatically notify related side effects for re-execution when data changes. Creating a reactive object uses the `reactive` function, which internally calls `createReactiveObject` to set up Proxy get/set traps. In the getter, the `track` function establishes the relationship between properties and side effects, while in the setter, the `trigger` function triggers updates to the side effects. The `effect` function is used to register and maintain an `effectStack` to handle nested effects. Array methods require special handling, such as tracking `length` changes. Scheduling execution allows for deferred triggering. Computed properties are based on lazy execution of `effect`, and `watch` is implemented using `effect` and a scheduler. The system optimizes performance through hierarchical mechanisms to avoid repeated triggers and batch updates.

The implementation mechanism of reactive and ref

In Vue 3's reactivity system, `reactive` and `ref` are core APIs designed to handle objects and primitive data types respectively. Both rely on Proxy and dependency tracking mechanisms at their core but differ in implementation. `reactive` uses Proxy to intercept `get` and `set` operations on objects, enabling dependency collection and update triggering, with support for deep reactivity and special handling for array methods. `ref` wraps primitive values in an object, accessing the actual value via the `value` property, while object types are converted to `reactive`. In templates, `ref` is automatically unwrapped. Performance-wise, `ref` is more efficient for primitive types. The type systems differ, and their destructuring behaviors also vary. The underlying dependency tracking system manages dependencies through `track` and `trigger` functions. Special cases include `readonly` and `shallowReactive`. Vue 3.3 introduced reactivity transform to simplify syntax, working alongside the Composition API to provide a more flexible state management solution.

Setup of source code debugging environment

To set up a Vue 3 source code debugging environment, you need to prepare Node.js, pnpm, Chrome, and VSCode. First, install pnpm globally, then clone the Vue 3 source code repository and switch to a stable branch. Install dependencies, modify the Rollup configuration to generate source maps, and execute the build. Create a debug example HTML file, configure Chrome debugging, and set up `launch.json` in VSCode. Start a local server, with key breakpoints set in the reactivity system and component mounting process. Custom builds for specific modules can be debugged directly, and Jest test cases can be debugged by combining browser developer tools for source mapping and performance analysis. If issues arise, check source map generation, breakpoint paths, or dependency version conflicts.

The main differences compared to the Vue 2 architecture

Vue 3 has undergone a comprehensive upgrade compared to Vue 2, replacing `Object.defineProperty` with `Proxy` to implement the reactivity system, eliminating the need for recursive property traversal and supporting direct assignment of new properties. The Composition API organizes code through the `setup` function, addressing logic fragmentation issues. The virtual DOM has been optimized with static hoisting and patch flags to enhance performance. TypeScript support has been improved, offering better type inference. Global APIs have been adjusted to application instance APIs, and lifecycle hooks have been renamed, with new debugging hooks added. `v-model` now supports multiple bindings, and new components like `Teleport` and `Suspense` have been introduced. Single-file components support multiple root nodes and the `setup` syntactic sugar. Transition and animation class names have been improved, while some event APIs and methods have been removed. The plugin system has been changed to application instance installation. Overall, Vue 3 offers better performance, a smaller bundle size, faster rendering, and lower memory usage.

The general approach to performance optimization

Vue 3 has undergone comprehensive performance optimizations, including compile-time improvements such as static hoisting, patch flags, and tree flattening, as well as runtime enhancements like a faster virtual DOM and a lightweight reactivity system. The reactivity system has been refactored to use Proxy for lazy reactivity and fine-grained dependency tracking. Component rendering optimizations include support for Fragment, Teleport, and Suspense. Memory management has been improved for better garbage collection (GC) friendliness and reduced runtime footprint. Developer tools integration provides precise performance analysis and time-travel debugging. In practice, developers can use `v-memo` to avoid unnecessary reactivity updates and leverage computed properties efficiently. Performance monitoring features include rendering performance profiling, custom performance markers, and memory leak detection.

The importance of TypeScript support

TypeScript plays a crucial role in the Vue 3 ecosystem by significantly improving the maintainability of large-scale projects through its type system and static checks. The Composition API in Vue 3 deeply integrates with TypeScript, enabling precise type inference for component props and Composition API utilities like `ref` and `reactive`. At the source code level, generics and conditional types are employed to design component instances and template compiler type utilities. The toolchain integration, including `vue-tsc` and the Volar plugin, provides template type checking and code hints. Type extension mechanisms support global type augmentation, while type information aids in performance optimization through static analysis and reactive system enhancements. In complex scenarios like cross-component communication and SSR, types ensure consistency. Type-documentation synergy is achieved via TSDoc for API documentation generation. Ecosystem libraries must provide type definitions to ensure a complete development experience. TypeScript enhances Vue 3's development efficiency and code quality across multiple dimensions.

Optimization strategies for the virtual DOM

Vue3's virtual DOM mechanism significantly improves performance through compile-time and runtime optimizations. Static hoisting during compilation extracts unchanged nodes outside the render function to avoid repeated creation. PatchFlags mark dynamic content for quick identification during the Diff process, skipping static comparisons. BlockTree divides dynamic blocks and works with dynamic anchors to precisely locate changes. Event caching prevents repeated function creation. Static type analysis identifies optimization opportunities. An efficient Diff algorithm handles complex sequences with dual-end comparison. The reactive system ensures DOM updates only trigger upon data changes. Together, these optimizations build Vue3's high-performance rendering system.

The design philosophy of the Composition API

Vue 3's Composition API is a revolutionary innovation that transforms the way components are organized. It addresses the issue of logic fragmentation in the traditional Options API by centralizing related logic within the `setup` function. The Composition API offers better TypeScript support, providing clear type declarations and enabling true logic reusability. By replacing mixins with composable functions, it deeply integrates the reactivity system, building on `ref` and `reactive` as foundations. It unifies lifecycle hooks into functional forms and can coexist with the Options API, facilitating migration. The Composition API also enables compiler optimizations and encourages breaking down complex logic into smaller composable functions. These functions can be used outside components, simplifying testing. With a rich set of reactive utility functions and deep template integration, it streamlines state management and improves dependency injection. The API has spurred a custom hook ecosystem, promoting a declarative programming style. Features like `watchEffect` automatically track dependencies, significantly enhancing code organization and maintenance efficiency.

The separation design between compilation and runtime

Vue 3 adopts a design architecture that separates compile-time and runtime to enhance framework flexibility. During the compilation phase, templates are transformed into optimized render functions, including parsing templates into AST, static analysis, and code generation. The runtime is responsible for executing render functions, handling the virtual DOM, and managing reactive data. This separation results in a smaller runtime size, better performance, and flexible build options. The compiler performs optimizations like static hoisting to reduce runtime overhead, while the runtime efficiently updates the DOM based on compilation hints. The design supports custom renderers and server-side rendering. The compiler can detect template errors and seamlessly integrates with the reactive system, combined with TypeScript to provide type safety. The overall architecture achieves an efficient development experience through compile-time optimizations and runtime collaboration.