Changes in component template refs

In Vue.js, the `ref` attribute is used to directly access DOM elements or child component instances. Vue 3's Composition API optimizes the usage of `ref`. In Vue 2, it is accessed via `this.$refs`, while in Vue 3's `<script setup>`, you can directly declare a `ref` variable. When combining `ref` with `v-for` in the Composition API, a function form is required to collect references. Dynamic `ref` names can be implemented using variables or functions. In TypeScript projects, type annotations can be added to `ref`. Components control exposed content via `defineExpose`. For performance, avoid excessive use of `ref`. Note that conditionally rendered `ref`s should be accessed after `nextTick`. The behavior of `ref` remains consistent in `Teleport` and `KeepAlive` scenarios. In render functions, `ref` must be passed via parameters. When custom directives and `ref` coexist, pay attention to their execution order.

Component performance optimization (shouldUpdateComponent)

In Vue, `shouldUpdateComponent` is used to optimize performance by controlling child component updates. By default, components re-render when props or state change. This feature acts as a gatekeeper in the virtual DOM diffing process, determining whether to proceed with updates. It is suitable for scenarios like list rendering and form controls. Compared to React's `PureComponent`, it offers greater flexibility but requires manual implementation. Care must be taken with reference-type data comparisons. It can work in tandem with computed properties. Advanced applications include route optimization and animation performance control. Performance testing can be done using DevTools. In Vue 3, similar functionality can be achieved via the Composition API. For large projects, higher-order components can be created to uniformly handle update logic. Proper use can significantly improve application performance, but the correctness of comparison logic must be ensured.

Component style scoping (:deep/:slotted/:global)

In Vue single-file components, style scoped achieves style isolation through the `data-v` attribute but has limitations when modifying child component slot content and global styles. To address this, the `deep`, `slotted`, and `global` selectors are provided. `deep` is used to penetrate scoped styles and modify child component internal styles, replacing Vue 2's `/deep/` or `>>>`. `slotted` is used to style slotted content, while `global` defines global styles. The article details the usage scenarios, syntax examples, and compiled effects of these selectors, along with tips for combining them, performance optimization suggestions, and solutions to common issues. It also compares other technical solutions like CSS Modules and introduces new features in Vue 3.3 and related configurations in build tools.

Context exposure (expose API)

The context exposure mechanism in Vue.js allows components to selectively expose internal states and methods to parent components through the `expose` option or the `defineExpose` macro. In the Composition API, using the `setup` function exposes all content by default, but this can be restricted using `defineExpose`. In the Options API, the `expose` option specifies accessible content. Parent components access the exposed APIs of child components via template refs. Common use cases include form validation and complex component control. Unlike `provide/inject`, `expose` focuses on parent-child component communication. The article also covers TypeScript support, dynamic exposure in advanced patterns, performance considerations, and comparisons with other frameworks. Finally, it provides debugging tips to help developers inspect the APIs exposed by components.

Improve component props type validation

In the context of expanding project scale and the widespread adoption of TypeScript, traditional prop validation methods in Vue.js components reveal shortcomings such as insufficient type hints and runtime overhead. Traditional prop validation suffers from tight coupling between type definitions and runtime checks, lacks support for complex type hints, fails to provide type hints in templates, and incurs performance costs due to validation logic. Vue 3's `defineProps` macro, combined with TypeScript, enables compile-time type checking, delivers full IDE support, handles complex types, and incurs zero runtime overhead. For scenarios requiring dynamic validation, it can be paired with `withDefaults` and runtime checks. Leveraging TypeScript's advanced features, it supports conditional types and generic components, enabling powerful prop typing. When integrated with the Composition API, it maintains a complete type chain, including props-derived state and emit event types. Improvements to the type system enhance performance by reducing runtime check overhead and providing more precise type hints. A recommended migration strategy involves incrementally adding type annotations to existing props and transitioning to pure type definitions. A type-safe event system enables strict validation of emit event payloads, and type-safe prop utility functions can be created. Additionally, TypeScript types can automate documentation generation and handle edge cases like dynamic components and recursive types.

The component emits option

In Vue.js, the `emits` option is used to explicitly declare the events a component can trigger, supporting both array and object formats. The object format allows for the addition of validation functions. Using `emits` aids in component self-documentation, type checking, and runtime validation. In Vue 3, undeclared events are treated as native events. `emits` is often paired with `props` to facilitate parent-child component communication. In TypeScript, precise event payload types can be defined. It is recommended to use kebab-case for event names to avoid conflicts with native events. Validation functions can perform complex logic checks. In the Composition API, events are triggered via the `emit` parameter in `setup`. Vue 3 supports multiple `v-model` bindings, where `emits` plays a key role. During testing, event triggering can be verified. `emits` can also be used to encapsulate third-party library events or replace the event bus pattern. Dynamic event names must be declared in advance. Note the distinction between native events and custom events. Event parameters can be destructured or passed through slots.

Changes in the definition of async components (defineAsyncComponent)

In Vue 3, the definition of asynchronous components is achieved through `defineAsyncComponent`, replacing Vue 2's import syntax. This API provides basic usage and advanced configuration options, including loading state handling, error boundaries, and integration with Suspense. It supports dynamic imports and code splitting, can be directly used in the Composition API, and integrates with routing and state management. Special handling is required for SSR environments, and testing must account for asynchronous behavior. In TypeScript, it offers full type support and is suitable for modular loading and performance optimization scenarios in large-scale applications.

Upgrade component v-model (support multiple v-models)

Vue 3 significantly upgraded component v-model by supporting multiple v-model bindings, addressing the limitation of single binding in Vue 2. Through the v-model argument syntax, it enables multi-data flow control, requiring components to handle props and emit events separately for each parameter. This proves particularly useful in complex form scenarios while also supporting custom modifier processing as a replacement for Vue 2's .sync modifier. The article elaborates on the implementation principles, application scenarios, and integration with Composition API and TypeScript, providing performance optimization suggestions and common issue solutions. It demonstrates how to collaborate with features like provide/inject, offering developers more powerful tools for handling complex component communication.

Composition API component writing style

Vue 3's Composition API addresses the code fragmentation issue of the Options API in complex components by centralizing reactive data and logic management through the `setup` function. Core concepts include creating reactive data using `ref` and `reactive`, enabling logic reuse via composable functions, and providing lifecycle-equivalent hooks. Compared to the Options API, it offers better code organization and TypeScript support. The article details advanced usage such as props handling, state management integration, and asynchronous operations, along with solutions to common issues like reactive value loss, template refs, and dependency injection. Finally, it shares performance optimization techniques, third-party library integration methods, and best practices for enterprise-level application architecture, including layered design, global state management, and routing control.

Changes in Vue 3 component registration

Vue 3 has introduced several significant improvements in component registration: global component registration is now done via the `app.component` method, supporting multiple coexisting applications; local component registration is more flexible in the Composition API; async components are defined using the new `defineAsyncComponent` API; component naming recommends PascalCase; dynamic components require distinguishing between components and native elements; functional components must be explicitly defined, and the `functional` option is no longer supported; `v-model` supports multiple bindings and custom modifiers; custom elements are configured via `compilerOptions`; component inheritance removes `listeners` and the `native` modifier; component instance properties have changed; recursive components require explicit naming; scoped styles have been optimized; TypeScript support is enhanced; and component performance is improved, including reduced impact of global registration and lower overhead for functional components.