Vue3 Technology Sharing

Background and Significance of Vue 3#

With the rapid development of front-end technology, developers have higher demands for frameworks: they require better performance and improved development experience, as well as support for more features. In this context, the superior Vue 3 was born:

1. Better Performance: Vue 3 adopts a restructured reactive system and optimized template compiler, resulting in a significant performance improvement compared to Vue 2, with rendering performance increased by about 1.5-3 times.

2. Better Development Experience: Vue 3 has made improvements in syntax, type inference, and lifecycle, providing a better development experience. It also introduces new features such as the Composition API, allowing for more flexible organization of code and logic.

3. More Features: Vue 3 adds new features like Portals, Teleport, and Suspense, providing better solutions for scenarios involving component reuse and asynchronous rendering.

Issues with Vue 2#

Vue 2 is a very excellent and popular front-end JavaScript framework, but it also has some issues:

1. Poor Readability and Maintainability: Vue 2 uses the Options API to define components and scatters related logic across different lifecycle functions, making component logic difficult to read and maintain. This can be particularly troublesome for complex components during development, debugging, and testing.

2. Static Type Checking Issues: Vue 2 does not natively support static type checking, which brings significant trouble during project development and maintenance. Although third-party tools like TypeScript or Flow can be used to address this issue, they may require considerable additional investment in deployment, learning, and usage.

3. Performance Issues: Vue 2's virtual DOM can experience performance issues when handling a large number of data changes. Additionally, there are flaws in the template compiler that somewhat reduce the framework's performance.

Goals and Advantages of Vue 3#

1. Higher Performance: Vue 3 has restructured the reactive system and virtual DOM implementation, improving overall performance. For instance, rendering performance has increased by about 1.5-3 times, and memory usage is more lightweight.

2. Better TypeScript Support: Vue 3 provides more comprehensive TypeScript support, allowing for type checking to catch errors and issues in the code, enhancing code robustness and readability. The combination of TypeScript and the Composition API can lead to better code organization and maintainability.

3. More Flexible Component Development: Vue 3 eliminates the option-based API that existed in Vue 2 and introduces the Composition API, which can essentially replace the Options API, making it more flexible and efficient for developers to create components based on functions.

4. Better Development Tool Support: Vue 3 has fully updated related DevTools and documentation, including upgrades in areas like Vuex and VueRouter.

5. Smaller Package Size: Vue 3 removes some outdated and deprecated APIs, resulting in a smaller bundled size, making it easier to set up other projects.

In summary, Vue 3 focuses on design, with significant improvements in almost every aspect. It offers more features, guarantees type safety, and has additional advantages such as faster rendering speed and reduced memory usage.

Overview of New Features in Vue 3#

Improvements to the Reactive System#

In Vue 2, the reactive system hijacks properties through Object.defineProperty, achieving two-way binding between data and views. However, this implementation has clear drawbacks: it cannot listen to array changes, getter/setter processing can be slow in some cases, and it cannot monitor deeply nested objects.

To address this, Vue 3 uses the Proxy API to replace Object.defineProperty for implementing reactive data binding. Compared to the former, Proxy can monitor all types of property modifications, does not rely on any language runtime limitations, and has better performance. Additionally, since Proxy can directly intercept assignment operations, it avoids issues like Traps. Proxy also supports Map, Set, Weakmap, and Weakset.

Vue 3 also eliminates the watch method and $set/delete methods from Vue 2, with the former replaced by watchEffect and watch, while the latter can use native JavaScript APIs (like Array#splice) to manipulate reactive objects.

Faster Rendering Performance#

1. Compile-time Optimization: Vue 3 uses static analysis of templates during the compilation phase to generate more optimized code at runtime, improving performance, such as Hoist Static and Cache Handlers.

2. Faster Internal Algorithm: Vue 3 rewrites the virtual DOM rendering engine and employs hoisting techniques, significantly reducing redundant operations during the virtual DOM update process. To lighten the patch process, it generally avoids complex nesting or using dynamic keys and unnecessary computation.

3. Functional Component-oriented Design: Vue 3 provides more complete and native support for functional components, with the generated render functions being simpler than those in Vue 2, reducing some small scripts.

Smaller Package Size#

This is mainly achieved through the following methods:

1. Finer-grained Modularity: The core library is split into multiple smaller modules, allowing users to only import the necessary modules instead of the entire library, reducing the package size.

2. Tree-shaking Support: Vue 3 is compatible with modern bundlers' dependency analysis mechanisms, automatically removing unused code to minimize the size of the bundled files.

3. Removal of Unnecessary Features and APIs: Vue 3 removes some rarely used or nearly unused features and APIs from Vue 2, such as Inline Template and Filters.

4. Native ES Module Exports and pure function encapsulation to avoid runtime data checks.

Better TypeScript Support#

Significant improvements have been made in TypeScript support, mainly reflected in the following aspects:

1. Composition API: The Composition API introduced in Vue 3 better supports TypeScript's type inference. When writing components using the Composition API, developers can use generics and interfaces to facilitate type checking.

2. Built-in Definition Files: Vue 3's source code comes with comprehensive TypeScript definition files and also supports Vue 2's type definition files on DefinitelyTyped, which can be imported and used by directly installing the @vue/runtime-core package.

3. Supporting Development Toolchain: Tools like Vue CLI and Vue Devtools provide good support for TypeScript, automatically generating corresponding TypeScript type definition files for easier code editing and debugging.

4. Prop Type Validation: In Vue 3, developers can set the type of Props or use TypeScript's interface and type syntax for Prop type validation.

Composition API#

The Vue 3 Composition API is a way to organize component code based on functions rather than option objects, providing finer-grained methods to organize logic code within components, including the following main features:

1. reactive and computed: Create reactive data and define computed properties using reactive and computed.

2. Lifecycle Hooks: Use onMounted, onUpdated, and other hook functions to replace lifecycle functions in Vue 2.

3. ref: A tool for wrapping variables to make them reactive, such as the value property of input elements.

4. watch and watchEffect: watch is used to listen for changes in a reactive data and perform corresponding operations, while watchEffect automatically tracks its dependencies reactively.

5. provide and inject: The combination of provide and inject can achieve cross-level data passing.

Better Accessibility Support#

There have been improvements in accessibility support, including the following enhancements:

Custom Accessible Landmarks: Vue 3 provides a richer and easier-to-use Accessible Landmarks feature, with semantic structure and better attention to users with disabilities.
New v-model API: The v-model API in Vue 3 can accept custom setter validators in input or textarea, ensuring that the values bound to the component's model meet given rules, which greatly helps in supporting input data quality and error capture in code.
Improved ARIA Element Markup Accessibility: Vue 3 provides a simpler and more intuitive way to manage ARIA element markup, supporting modern standards and better connecting with other semantic structures, improving screen reader parsing.
Better TypeScript type safety: TypeScript types help avoid many type errors, improving code readability and maintainability, and making it easier to find documentation for properties and methods.
Accessibility support in SSR mode: Compared to Vue 2, Vue 3 has made many important improvements in server-side rendering (SSR), such as providing efficient code splitting methods between client and server and better header response handling.

Improvements to the Reactive System#

Use of Proxy#

The main technology is utilizing the Proxy object in ECMAScript 6. The proxy object can intercept property assignments and accesses, providing better performance optimization in specific scenarios. The improvements in Vue 3's reactive system using Proxy are as follows:

Directly listen to ordinary JavaScript objects: Vue 3 can directly listen to changes in ordinary JavaScript objects, no longer relying on Object.defineProperty(), allowing Vue 3 to support more data structures and types.
Faster initialization and rendering speed: Vue 3 caches related elements in the internally referenced Proxy object, providing good initial performance and optimizing during component unmounting.
Reduce useless executions: Vue 3 injects as much information as possible during template compilation to mark dependencies, better reducing unnecessary re-renders.

Optimizations to Dependency Tracking Mechanism#

Compared to Vue 2, Vue 3 improves the implementation of the dependency tracking mechanism, reducing unnecessary computations and improving performance, with specific details as follows:

Dependency tracking implemented by Proxy objects: Vue 3 uses the new Proxy API to implement the dependency tracking mechanism, which is faster than Vue 2's Object.defineProperty() because it provides more reflection properties and traps.
Cache results produced by component render functions: Vue 3 caches intermediate results produced by render functions, recalculating only when reactive data changes, thus avoiding unnecessary computations and waste.
Optimize server-side rendering through SSR: Vue 3 introduces a method called Static Site Generation to address the slow initial data loading issue in SSR, allowing front-end developers to obtain fully rendered HTML files during the build phase, effectively avoiding initial data requests from the server and reducing the first screen rendering wait time.

Optimized computed and watch#

computed#

In Vue 3, computed properties are registered with the reactive system using fixed getter/setter functions. Unlike Vue 2, Vue 3 uses caching to record whether the computed property calculation result has been used.
When the dependent data of computed changes, the computed will be marked as 'dirty' and wait for updates through the scheduling function. It will only be recalculated and cached when the computed property is read, making computed properties more efficient, predictable, and traceable.

watch#

In Vue 3, watch benefits from the new scheduler API. The scheduler allows developers to finely control the way and timing of asynchronous behavior according to their needs.
By writing custom schedulers, developers can choose to disable automatic callback execution or suspend its execution until the next frame. Additionally, developers can ensure that callbacks are never executed repeatedly and set a maximum queue length to prevent infinite queuing.
In summary, Vue 3 has made corresponding optimizations to both computed and watch. For computed, the optimization mainly involves using caching to enhance performance; for watch, the new scheduler API is adopted to control asynchronous behavior, improving efficiency and controllability in specific scenarios.

Faster Rendering Performance#

Static Tree Hoisting#

Static Tree Hoisting refers to the process of converting nodes in a dynamically generated virtual DOM tree that do not need to be frequently updated from dynamic nodes to static nodes. In Vue 3, static tree hoisting is implemented by the compiler, mainly optimizing runtime performance through two methods:

1. Static Node Hoisting

For immutable static nodes, Vue 3 automatically marks them as static nodes, allowing these nodes to be reused during each repaint, thus avoiding unnecessary recreation and destruction. This significantly reduces the complexity of internal algorithms and CPU usage of the application.

2. Static Property Hoisting

For dynamic nodes containing static properties (like class and style), the Vue 3 compiler also automatically hoists them as static properties, eliminating the need to recalculate these static properties during component execution.

Patch Flag and Static Props Hoisting#

1. Patch Flag

In Vue 2, when data changes, the virtual DOM needs to compare new and old nodes to determine which nodes need to be updated. This process is called the "Diff algorithm," which requires traversing the entire tree structure, significantly affecting performance. Vue 3 proposes a new virtual DOM optimization scheme - Patch Flag.

Patch Flag marks elements or components with dynamic binding directives according to their change characteristics, allowing the Virtual DOM to only consider elements or components with Patch Flags during diff comparisons. This significantly reduces redundant calculations and unnecessary DOM operations, thus improving rendering performance.

2. Static Props Hoisting

In Vue 2, static properties are recreated every time a component is re-rendered, causing unnecessary performance waste. Vue 3 introduces "Static Props Hoisting," allowing the renderer to extract properties that will never change during the compilation phase and directly apply them to the rendering results, eliminating the need to recalculate them when rendering the next component.

Both schemes are implemented at compile time, reducing the time and performance overhead required for rendering, thus granting Vue 3 faster rendering speed and higher efficiency.

Cache Handlers#

Optimizing component performance by caching event handler functions.

In Vue 2, a new handler function needs to be created for each event listener during every re-render, which may lead to a large number of unnecessary function instantiations. In Vue 3, event caching can avoid this situation.

When a component transitions from an active state to a non-active state (e.g., when a v-if condition is not met), Vue destroys all its event handler functions. If the component re-enters an active state (e.g., when the condition becomes true), Vue 3 can reuse the previously cached handler functions, thus reducing the overhead of inserting and removing event listeners.

The specific implementation involves maintaining a PatchFlag within the component to indicate whether a component has cached events, ensuring that cached events are updated while ensuring correct event triggering.

Overall, event caching allows the same event handler to be reused when the component is rendered multiple times, significantly reducing unnecessary function instantiations and improving application performance.

Memory Management Optimization#

1. Static Marking

In Vue 3, static marking technology allows some static content, such as templates, directives, and styles, to be precompiled and initially rendered at application startup. This processing method reduces the need to repeatedly parse and create static content, significantly decreasing memory usage.

2. Static Hoisting

Static hoisting is another optimization measure that identifies reusable parts within the static content of components and extracts them from the HTML template. This not only optimizes component rendering performance but also saves memory space.

3. Batch Updates

Vue 3's update mechanism adopts batch updates to reduce unnecessary DOM operations and computations. Vue 3 caches all values to be updated until it needs to update the view, thus avoiding repeated computations and rendering operations.

4. Zero Proxy

Vue 3's reactive objects use zero proxy technology, meaning that new reactive objects or wrapped functions are only created when getters or setters are called. This approach reduces memory usage and increases code execution efficiency.

5. Async Handling

Asynchronous rendering in Vue 3 can greatly enhance application performance. By processing time-consuming operations, such as component rendering and data changes, in asynchronous threads, it reduces main thread blocking, avoiding lag during user operations and improving application responsiveness.

6. Tree Shaking

To maintain a lightweight framework and avoid bundling unnecessary code into the final build, Vue 3 employs Tree Shaking technology. This technique removes unused modules or functions in JavaScript that are not referenced, only packaging the directly referenced code, resulting in smaller application sizes and faster execution.

7. Compilation Caching

Vue 3 introduces compilation caching at the compiler level, allowing already compiled templates to be cached. When running again, it first checks the cache for the corresponding compilation result; if not found, it recompiles. This feature can significantly improve application startup speed.

Better TypeScript Support#

Type Inference and Type Checking#

1. Type Inference

Vue 3 supports type inference to reduce type annotations in the code. This allows developers to write cleaner and clearer code without needing to add explicit type declarations for every variable, function parameter, and return value.

2. Type Checking

Vue 3 uses TypeScript for syntax parsing and type checking, allowing for early detection and capture of potential type errors and coding issues. Common type checking scenarios include prop type checking and component event type checking.

Type Declaration Files#

1. Complete Type Declaration Files

Vue 3 provides complete TypeScript type declaration files, enabling the construction of truly TypeScript applications while ensuring type safety during development through the compiler.

2. Support for Vue Components

The Vue 3 type declaration files also support Vue components, including type definitions and validations for component props and template directives, greatly simplifying the component development process and avoiding time-consuming debugging due to type errors.

3. Support for Object Merging

The Vue 3 type declaration files also support extending types through object merging. This feature is suitable for unconventional application scenarios, such as handling dependency injection, plugins, and mixins that may modify component options.

4. Support for Class Components

The Vue 3 type declaration files also support Vue's Class Components. Class components can be seen as a variant of ordinary components, using the component options API, but methods and lifecycle hooks appear more like static methods and instance functions of classes.

Composition API#

Differences from Options API#

The main differences are as follows:

1. Data and Logic Reuse

An Options API component contains multiple parts, including templates, styles, and JavaScript code. Data and methods defined within the component can only be used by the template and JavaScript code within that component.

The Composition API allows handling the same logical block through separate functions, which can be combined for reuse. This mechanism enables similar functionalities to be reused across multiple components, avoiding the large amount of duplicate code that can occur with the Options API.

2. Support for Type Definitions

The Options API supports TypeScript type definitions, but the types are limited to specific option objects or lifecycle functions.

The Composition API allows for accurate static type checking of function parameters and return values using TypeScript capabilities. This helps ensure that the application does not encounter runtime type errors.

3. Lifecycle Hooks

In the Options API, lifecycle hook functions are distributed across different lifecycle stages. Therefore, managing code with the Options API can lead to logical confusion and loose code organization.

The Composition API provides more expressive and readable lifecycle hook functions, such as onMounted, onUpdated, and onUnmounted, offering better support for component development.

4. Other Technical Features

The Composition API allows for reusable state logic through exported constants, enabling the construction of plugin-based custom logic libraries. This is similar to Mixins and HOCs in Vue 2.x, but with more powerful features due to dependency injection, namespaces, etc.

Usage of the setup Function#

In Vue 3, the setup function is the entry point for components, used to configure components, with the following features:

1. Access to Props and Context

The setup function can access the component's props and obtain the component's context (context) through the second parameter, such as $attrs, $emit, $slots, $refs, etc.

2. Reactive Data Handling

Vue 3 introduces new reactive APIs like ref and reactive, allowing variables to be made reactive within the setup function, and these data can be directly used in templates. For example:

<script>
import { ref } from 'vue'

export default {
    setup() {
        const count = ref(0)
        return {
            count
        }
    }
}
</script>

// Using the count variable in the template

<template>
    <div>{{ count }}</div>
</template>

3. Recommended Use of Object Return Values

The setup function is recommended to return an object, making it clearer to expose the internal variables and methods of the component.

4. Lifecycle Hooks

Lifecycle hooks such as onMounted, onUpdated, and onUnmounted can be used within the setup function.

5. Computed Properties and Watchers

Computed properties and watchers can be declared within the setup function. Computed properties need to be created using the computed function, while watchers need to be created using the watch function.

import { reactive, computed, watch } from 'vue'

export default {
    setup(props) {
        const state = reactive({
            count: 0,
            doubleCount: computed(() => state.count * 2)
        })

        watch(
            () => props.userId,
            (userId) => {
                // Handle changes in userId
            }
        )

        return {
            ...toRefs(state)
        }
    }
}

Usage of ref and reactive#

In Vue 3, ref and reactive are used to create reactive data. Their main differences are as follows:

1. ref

ref is used to wrap a non-reactive data type, such as a primitive type or object. After using ref, the data can be accessed via .value, and this data behaves reactively.

import { ref } from 'vue'
const count = ref(0)
console.log(count.value) // Outputs 0
count.value++ // Modifies the data
console.log(count.value) // Outputs 1

2. reactive

reactive is used to wrap a plain object, making it reactive. After using reactive, changes to the properties of that plain object will trigger re-renders of components that depend on that property.

import { reactive } from 'vue'

const state = reactive({
    name: 'John Doe',
    age: 18
})

console.log(state.name) // Outputs "John Doe"
state.age++ // Modifies the data
console.log(state.age) // Outputs 19

It is important to note that data created with reactive needs to access all properties using dot notation. From a performance perspective, it is advisable to avoid creating deeply nested reactive objects.

For example, defining too many nested objects within a reactive object can impact the performance of the entire application. Usage should be based on specific business scenarios.

In summary, both ref and reactive are APIs used in Vue 3 to create reactive data, with ref suitable for direct wrapping of primitive types or objects, while reactive is suitable for wrapping plain objects. Care should be taken to avoid performance issues and to use dot notation for data access and modification.

Custom Hook Functions#

In Vue 3, we can reuse component logic through custom hook functions, similar to React hooks. A custom hook function is essentially a function that returns an object, defining the required data and methods.

For example, we can create a hook function named useCount to encapsulate counter logic. First, define the hook function:

import { reactive, computed } from 'vue'

export default function useCount() {
    const state = reactive({
        count: 0
    })

    const doubleCount = computed(() => state.count * 2)

    const increment = () => {
        state.count++
    }

    return {
        state,
        doubleCount,
        increment
    }
}

Then, use the custom hook function within a component:

<template>
    <div>
        <p>Counter: {{ count }} (Double: {{ doubleCount }})</p>
        <button @click="increment">Add One</button>
    </div>
</template>

<script>
import { defineComponent } from 'vue'
import useCount from './useCount'

export default defineComponent({
    setup() {
        const { state, doubleCount, increment } = useCount()
        return {
            count: state.count,
            doubleCount,
            increment
        }
    }
})
</script>

This way, we can reuse the useCount hook function in other components without having to rewrite the counter-related code.

It is important to note that custom hook functions can only be used within the setup function, as only in setup can we access the component's context and lifecycle hook functions.

Better Accessibility Support#

Support for ARIA Attributes#

Vue 3 provides better accessibility support, including support for ARIA attributes. ARIA (Accessible Rich Internet Applications) is a set of properties and states developed for users with disabilities, improving the accessibility of web applications.

In Vue 3, we can set ARIA attributes using the v-bind directive, for example:

<button v-bind="{ 'aria-label': 'Close Dialog', 'aria-disabled': isDisabled }">Close</button>

In the above code, we use v-bind to bind two ARIA attributes: aria-label and aria-disabled. The aria-label specifies the text alternative for the button, while aria-disabled indicates whether the button is disabled.

Additionally, Vue 3 provides built-in ARIA helper functions, making it easier to manage ARIA attributes. For example, the v-bind directive also offers a shorthand syntax .bind() for binding multiple ARIA attributes to the same element:

<button :aria-label="getCloseLabel()" :aria-disabled="isDisabled">Close</button>

In this code, we use the shorthand syntax and to bind ARIA attributes, and we use another function getCloseLabel to dynamically obtain the button's text alternative.

Besides the v-bind directive, we can also use the v-on directive to set ARIA-related events, for example:

<button v-on="{ keydown: onKeydown }"></button>

In this code, we use v-on to bind the KeyDown event and handle it through the onKeydown function. In this process, ARIA attributes can be used to indicate operations like the rotation direction of an opened menu.

In summary, Vue 3 provides complete support for ARIA attributes, making it easier for us to develop web applications with good accessibility.

In web applications, keyboard navigation is crucial for users with disabilities and those using assistive devices.

Implementing keyboard navigation in Vue 3 typically involves the following three aspects:

Use the tabindex attribute to mark elements as focusable. For example, setting tabindex="0" on a button element makes it a focusable element.
Listen for keyboard events to handle keyboard navigation operations. For instance, we can listen for pressed key values in the keydown event and perform corresponding actions, such as jumping to the next or previous focusable element.
Set the aria-activedescendant attribute in the keyboard event handler to specify the ID of the currently focused element. This helps screen readers report information about the currently focused element to users.

Other Improvements and Optimizations#

Teleport Component#

The Teleport component helps us easily render components to other locations in the DOM structure. For example, suppose we have a modal component:

<template>
    <div class="modal">
        <h2>{{ title }}</h2>
        <p>{{ content }}</p>
        <button @click="closeModal">Close</button>
    </div>
</template>

<script>
export default {
    props: {
        title: String,
        content: String
    },
    methods: {
        closeModal() {
            this.$emit('close')
        }
    }
}
</script>

When using it, we can render the modal to another location, such as under the root element of the page, using the Teleport component:

<template>
    <div>
        <button @click="showModal()">Show Modal</button>

        <teleport to="body">
            <Modal v-if="isModalVisible" :title="modalTitle" :content="modalContent" @close="hideModal" />
        </teleport>
    </div>
</template>

<script>
import { ref } from 'vue'
import Modal from './Modal.vue'

export default {
    components: { Modal },
    setup() {
        const isModalVisible = ref(false)
        const modalTitle = ref('')
        const modalContent = ref('')

        function showModal() {
            modalTitle.value = 'Modal Title'
            modalContent.value = 'Modal Content'
            isModalVisible.value = true
        }

        function hideModal() {
            isModalVisible.value = false
        }

        return { isModalVisible, modalTitle, modalContent, showModal, hideModal }
    }
}
</script>

In the above code, we use the teleport component to render the modal under the root element of the page, achieving our requirement. In the usage of Teleport, we can specify the target location for rendering using the to attribute, such as specifying it as body.

In summary, the Teleport component in Vue 3 can help us easily render components to other locations, making it a very useful tool for developing applications that require dynamically inserting/moving components on the page.

Suspense Component#

The Suspense component helps us display alternative content while asynchronously loading components, providing a better user experience. For example, when using asynchronous components, we can use the Suspense component to show a loading prompt, letting users know that data is being loaded instead of displaying a blank page.

The following example demonstrates how to use Suspense with asynchronous components:

<template>
    <div>
        <h1>Async Component Demo</h1>

        <Suspense>
            <!-- Display asynchronous component -->
            <template #default>
                <AsyncComponent />
            </template>

            <!-- Display fallback content -->
            <template #fallback>
                <div>Loading...</div>
            </template>
        </Suspense>
    </div>
</template>

<script>
import { defineAsyncComponent } from 'vue'

const AsyncComponent = defineAsyncComponent(() => import('./components/AsyncComponent.vue'))

export default {
    components: {
        AsyncComponent
    }
}
</script>

In the above code, we first define the asynchronous component using the defineAsyncComponent function, and then wrap it with the Suspense component in the template, using the #fallback slot to provide alternative loading prompt information.

When the asynchronous component is loading, the default slot's content, which renders AsyncComponent, will be displayed; when the asynchronous component has not yet finished loading, the fallback content slot in Suspense will be displayed—here, the loading prompt.

It is important to note that the Suspense component can only have one default slot but can have multiple fallback content slots. In the default slot, only one asynchronous component or other content that needs to be loaded asynchronously can be placed.

Other API and Syntax Improvements#

Vue 3 also includes the following API and syntax improvements:

createApp Function: createApp is a new API for creating Vue applications. Unlike using new Vue() in Vue 2, Vue 3 requires first creating an application instance using the createApp function, on which components and other configurations are mounted.
Improved Template Compiler: In Vue 3, the template compiler has been rewritten, and the optimized new version can compile templates faster and generate smaller code packages.
Support for Dynamic Binding of directive names prefixed with "v-": In Vue 3, all directive names prefixed with "v-" can be dynamically bound using bracket notation. For example:

<div :[attribute]="value"></div>

Improved Reactivity System: Vue 3 has improved the performance efficiency of tracking reactive variables and supports reactive updates for complex data types like nested objects, Map, and Set.
New Lifecycle Methods: Vue 3 has introduced two new lifecycle methods, beforeUnmount and onRenderTracked, allowing developers to perform special operations and optimize code.
More Flexible Slots: Unlike the scoped slots in Vue 2, Vue 3's slots adopt a more flexible syntax. Slots can be defined using v-slot or #, and support named slots, scoped slots, and dynamic slots.
Introduction of Custom Renderer API: Developers can now use Vue's open custom renderer API to create custom renderers that render Vue in non-DOM tree environments like canvas.

Compatibility Issues with Vue 3#

Compatibility Issues with Vue 2#

Vue 3 has made many significant improvements in API and syntax compared to Vue 2, which can lead to some incompatibilities with Vue 2. The following are compatibility issues with Vue 3 and their solutions:

1. Asynchronous Components: In Vue 2, when introducing asynchronous components, you could use Promise in import() for lazy loading, but in Vue 3, you need to use the new defineAsyncComponent method to define asynchronous components. However, you can improve code flexibility through the setup function and Suspense component.

2. Filters: Common filters in Vue 2 have been deprecated; Vue 3 recommends using computed properties or functions instead.

3. Mixins: In Vue 2, developers could abstract some logic into mixins to simplify code within components. In Vue 3, mixins have been deprecated, and it is recommended to use the Composition API instead.

4. Removal of Listeners Property: In Vue 2, there was a listeners property that allowed parent components to inherit child component event listeners. In Vue 3, this property has been removed; please use v-on="$attrs" instead.

Compatibility Issues with Third-party Libraries#

Due to the significant improvements in API and syntax in Vue 3, some third-party libraries from Vue 2 may not work properly in Vue 3 or may require appropriate changes. The following are some third-party libraries that may be affected and their solutions:

1. Vuex

Vuex is a state management pattern and library for Vue applications. In Vue 3, Vuex has released a version compatible with Vue 3 to address compatibility issues, and developers can directly install the latest version from vuex@next.

2. Vue Router

Vue Router is a complete routing solution commonly used in single-page applications. In Vue 3, Vue Router has released the latest version (4.x) to support Vue 3, and developers can directly install this version from [email protected].

3. Element UI

Element UI is a desktop component library based on Vue.js 2.0. If your project uses Element UI, you need to upgrade to the new version (3.0) based on Vue 3 provided by the official, and developers can refer to the official documentation for changes.

4. Axios

Axios is a Promise-based HTTP library for sending HTTP requests in browser and Node.js environments. In Vue 3, the Axios library can still work normally, or you can use other similar third-party libraries as alternatives.

It is important to note that not every third-party library has been upgraded to a version compatible with Vue 3. If your project relies on specific third-party libraries, be sure to consult the documentation or communicate with the library's developers for more detailed information.

Summary and Outlook#

Advantages and Disadvantages of Vue 3#

Advantages:

1. Easy to Learn and Use: Compared to Angular and React, Vue 3's API design and syntax are simpler and easier to understand, reducing learning costs and development difficulties.

2. Reactive and Efficient: Vue 3's reactive system is implemented based on Proxy, offering higher performance and supporting dynamic property and array element additions, enhancing the development experience.

3. Composition API: Vue 3's Composition API provides better code organization, reusability, and testability, allowing for more flexible creation and better management of state and logic within Vue components.

4. Future-oriented Features: Vue 3 is more advanced in the JavaScript technology stack, using TypeScript, better supporting functional programming, and offering more comprehensive Types API.

5. Out-of-the-box Toolchain: Vue 3 provides a complete toolchain, such as Vue CLI, Vuex, and Vue Router, meeting various functional needs of developers.

Disadvantages:

1. Niche Market: Although the Vue framework is widely used in internet companies both domestically and internationally, its market share is smaller compared to Angular and React, resulting in a relatively smaller ecosystem and community.

2. Small Development Team: While the Vue.js core team is experienced, it is small in number and lacks full-time maintenance personnel.

3. Incomplete Ecosystem: Although Vue.js provides a rich set of surrounding tools, such as Vuex and Vue Router, compared to the large ecosystems of Angular and React, Vue's extension libraries may be lacking or not fully developed.

Future Development Directions#

The following are some potential development directions:

1. Better Performance: Vue 3 has already made significant improvements in performance, but there is still room for enhancement. In the future, it could explore using new technologies like WebAssembly or Workers to improve performance.

2. Better Composability: The Composition API allows developers to create composable components more easily and reuse code better. Future improvements may further enhance this API, increasing its functionality and flexibility.

3. Better Tool Support: As Vue 3 becomes more popular, tools will also become more flexible. For example, better development tools and plugins could be developed to help developers use Vue 3 more efficiently.

4. Better Cross-platform Support: Vue 3 already has the capability to be used in web, native, and desktop applications, and it may provide better support for other platforms in the future, such as VR and AR.

5. Richer Visualization Libraries: The Vue 3 ecosystem may develop more visualization libraries to meet different needs and provide better user experiences.