[译] 尤雨溪:Vue 3.0 计划
发布于 2个月前 作者 ab8512 2310 次浏览 来自 分享

<summary>展开原文</summary> Last week at Vue.js London I gave a brief sneak peek of what’s coming in the next major version of Vue. This post provides an in-depth overview of the plan.

上周,在Vue.js 伦敦会议上,我对 Vue 的下一个主版本将带来的东西做了一个粗略的介绍。这篇贴文则将提供一份关于这个计划的详细介绍。

为什么要出一个新的主版本?

<summary>展开原文</summary> Vue 2.0 was released exactly two years ago (how time flies!). During this period, the core has remained backwards compatible with five minor releases. We’ve accumulated a number of ideas that would bring improvements, but they were held off because they would result in breaking changes. At the same time, the JavaScript ecosystem and the language itself has been evolving rapidly. There are greatly improved tools that could enhance our workflow, and many new language features that could unlock simpler, more complete, and more efficient solutions to the problems Vue is trying to solve. What’s more exciting is that we are seeing ES2015 support becoming a baseline for all major evergreen browsers. Vue 3.0 aims to leverage these new language features to make Vue core smaller, faster, and more powerful. Vue 3.0 is currently in prototyping phase, and we have already implemented a runtime close to feature-parity with 2.x. Many of the items listed below are either already implemented, or confirmed to be feasible. Ones that are not yet implemented or still in exploration phase are marked with a *.

Vue 2.0 已经发布有整整两年了(时间过得可真快啊!)。在这段时期,Vue 发布了 5 个保持内核后向兼容的次要版本;我们积累了许多可以带来各种提升的点子,但是这些点子一直被搁置着,因为他们会带来打破兼容性的变动。与此同时,JavaScript 的生态系统及其本身也在急速地发展。许多工具的提升改善了我们的工作流,许多新语言特性给 Vue 一直在尝试解决的问题解锁了一些更简单、更全面、更高效的解决方案。更令人兴奋的是,我们看到了对 ES2015 的支持已经成为所有主流浏览器的基准。而 Vue 3.0 的目的就是借助这些新语言特性来让 Vue 的内核变得更小、更快、更强大。

Vue 3.0 已经在原型设计阶段了,而且我们已经实现了一个与 2.0 的特性近乎相等的运行时了。下文中列出的许多条目,要么已经实现了,要么已经确认可实现。那些还未实现或者仍在探索阶段的条目会用一个“*”标记

细节

高层 API 变动

一句话介绍:除渲染函数 API 和 scoped-slot 语法之外,其余均保持不变或者将通过另外构建一个兼容包来兼容 2.x。

<summary>展开原文</summary> Since it’s a new major, there is going to be some breaking changes. However, we take backwards compatibility seriously, so we want to start communicating these changes as soon as possible. Here’s the currently planned public API changes:
  • Template syntax will remain 99% the same. There may be small tweaks in scoped slots syntax, but other than that we have no plans to change anything else for templates.
  • 3.0 will support class-based components natively, with the aim to provide an API that is pleasant to use in native ES2015 without requiring any transpilation or stage-x features. Most current options will have a reasonable mapping in the class-based API. Stage-x features such as class fields and decorators can still be used optionally to enhance the authoring experience. In addition, the API is designed with TypeScript type inference in mind. The 3.x codebase will itself be written in TypeScript, and providing improved TypeScript support. (That said, usage of TypeScript in an application is still entirely optional.)
  • The 2.x object-based component format will still be supported by internally transforming the object to a corresponding class. Mixins will still be supported. *
  • Top level APIs will likely receive an overhaul to avoid globally mutating the Vue runtime when installing plugins. Instead, plugins will be applied and scoped to a component tree. This will make it easier to test components that rely on specific plugins, and also make it possible to mount multiple Vue applications on the same page with different plugins, but using the same Vue runtime. *
  • Functional components can finally be plain functions —however, async components will now need to be explicitly created via a helper function.
  • The part that will receive the most changes is the Virtual DOM format used in render functions. We are currently collecting feedback from major library authors and will be sharing more details as we are more confident of the changes, but as long as you don’t heavily rely on hand-written (non-JSX) render functions in your app, upgrading should be a reasonably straightforward process.

由于这次是一个新的主版本,所以会存在一些打破兼容的变动。不过,我们对后向兼容是非常重视的,所以我们希望能够尽快开始跟大家沟通这些变动。下面就是当前我们计划的公共 API 变动:

  • 模板语法的 99% 将保持不变。除了 scoped slot 语法可能会有一些微调之外,我们还没有任何其他针对模板的变动计划。
  • 3.0 版本将原生地支持基于 class 的组件,而且无需借助任何编译及各种 stage 阶段的特性,以此提供良好的编写体验。许多现有的 (组件) 配置项将有对应的合理的 class 版本的 API。各种 stage 阶段的特性,如 class 的静态字段和装饰器 (decorator) 等仍然可以选择性地使用,以此增强编写体验。另外,整体的 API 在设计时也将考虑 TypeScript 的类型推断特性。3.x 的代码库本身将用 TypeScript 来编写,并提供增强的 TypeScript 支持。(就是说,TypeScript 的使用与否仍然是整体可选的)
  • 2.x 系列的基于对象的组件格式仍将受支持,不过会在内部将其转换为一个相应的 class。
  • 仍然支持 Mixins。*
  • 为了避免在安装插件时造成对 Vue 的运行时的修改,顶层 API 可能会做一个大的翻修。到时,插件的作用域将只局限到具体的一个组件树,使得对那些依赖于某些具体插件的组件的测试变得容易,也会使得在同一个页面中挂载多个使用不同插件——但使用同一个 Vue 运行时——的 Vue 应用变为可能。*
  • 函数式组件将支持纯函数的书写形式——不过,这样的话异步组件就需要通过一个辅助性函数来显式地创建了。
  • 变动最大的部分将是渲染函数 (render) 中的虚拟DOM的格式。我们现在正在收集主流的第三方库的作者们的反馈,在对这些变动有了更多的信心之后,我们还会将更多的细节曝光;虽然变动较大,但是只要你没在你的应用中重度使用手写的渲染函数 (不是指 JSX),那么变动之后的升级应该会比较容易。

代码架构

一句话介绍:更优良的内部模块解耦;TypeScript;更易于贡献的代码库。

<summary>展开原文</summary> We are re-writing 3.0 from the ground up for a cleaner and more maintainable architecture, in particular trying to make it easier to contribute to. We are breaking some internal functionalities into individual packages in order to isolate the scope of complexity. For example, the observer module will become its own package, with its own public API and tests. Note this does not affect framework-level API— you will not have to manually import individual bits from multiple packages in order to use Vue. Instead, the final Vue package is assembled using these internal packages.

The codebase is also now written in TypeScript. Although this will make proficiency in TypeScript a pre-requisite for contributing to the new codebase, we believe the type information and IDE support will actually make it easier for a new contributor to make meaningful contributions.

Decoupling the observer and scheduler into separate packages also allows us to easily experiment with alternative implementations of these parts. For example, we can implement an IE11 compatible observer implementation with the same API, or an alternative scheduler that leverages requestIdleCallback to yield to the browser during long updates.*

在从零开始编写 3.0 之初,“达到更加清晰和更易维护的架构,特别是为了让代码的贡献变得容易”就是我们的目标。为了对复杂性进行隔离,我们将一些内部功能拆分为了多个单独的包。例如,observer 模块将成为一个单独的包,拥有自己对外的 API 和自己的测试用例;不过请注意,这不会对框架级的 API 造成影响——你不需要另外手动从多个包里导入许多小件小件的模块就可以使用 Vue,相反 Vue 的最终包会事先装配好这些内部包。

另外,代码库现在改为了用 TypeScript 编写;虽然这会使得“熟练TypeScript”成为对新代码库进行贡献的一个前置要求,不过我们相信有类型信息配合 IDE 的支持,对于一个新的贡献者来说,要做出有意义的贡献,实际上反而会更加容易。

将 observer 和 scheduler 解耦为分开的两个包后,我们还可以拿一些替代的实现对这两个包进行置换试验。例如,我们可以实现一个兼容 IE11、API 也相同的 observer;或者实现另外一种利用 requestIdleCallback 来在长耗时的更新中产出工作成果到浏览器的 scheduler。

<figure>img<figcaption></figcaption></figure>

监测机制

一句话介绍:更加全面、精准、高效;更具可调试性的响应跟踪;以及可用来创建响应式对象的 API。

<summary>展开原文</summary> 3.0 will ship with a Proxy-based observer implementation that provides reactivity tracking with full language coverage. This eliminates a number of limitations of Vue 2’s current implementation based on Object.defineProperty :

3.0 将带来一个基于 Proxy 的 observer 实现,它可以提供覆盖语言 (JavaScript——译注) 全范围的响应式能力,消除了当前 Vue 2 系列中基于 Object.defineProperty 所存在的一些局限,如:

  • 对属性的添加、删除动作的监测
  • 对数组基于下标的修改、对于 .length 修改的监测
  • 对 Map、Set、WeakMap 和 WeakSet 的支持
<summary>展开原文</summary> - Exposed API for creating observables. This offers a light-weight, dead simple cross-component state management solution for small to medium scale scenarios. - Lazy observation by default. In 2.x, any reactive data, regardless of how big it is, will be observed on startup. This can cause a noticeable overhead on app startup if your dataset is huge. In 3.x, only data used to render the initially visible part of your app will need to be observed, not to mention the observation itself is also much faster. - More precise change notification. An example: in 2.x, force adding a new property using Vue.set will cause any watcher that depends on the object to re-evaluate. In 3.x, only watchers that relies on that specific property will be notified. - Immutable observables: we can create “immutable” versions of a value that prevents mutations even on nested properties, except when the system temporarily unlocks it internally. This mechanism can be used to freeze passed-down props or Vuex state trees outside mutations. Better debugging capabilities: we can precisely trace when and why a component re-render is tracked or triggered using the new renderTracked and renderTriggered hooks:

另外这个新的 observer 还有以下特性:

  • 公开的用于创建 observable (即响应式对象——译注) 的 API。这为小型到中型的应用提供了一种轻量级的、极其简单的跨组件状态管理解决方案。(译注:在这之前我们可以通过另外 new Vue({data : {...}}) 来创建这里所谓的 observable;另外,其实 vuex 内部也是用这种方式来实现的)
  • 默认为惰性监测(Lazy Observation)。在 2.x 版本中,任何响应式数据,不管它的大小如何,都会在启动的时候被监测。如果你的数据量很大的话,在应用启动的时候,这就可能造成可观的性能消耗。而在 3.x 版本中,只有应用的初始可见部分所用到的数据会被监测,更不用说这种监测方案本身其实也是更加快的。
  • 更精准的变动通知。举个例子:在 2.x 系列中,通过 Vue.set 强制添加一个新的属性,将导致所有依赖于这个对象的 watch 函数都会被执行一次;而在 3.x 中,只有依赖于这个具体属性的 watch 函数会被通知到。
  • 不可变监测对象(Immutable observable):我们可以创建一个对象的“不可变”版本,以此来阻止对他的修改——包括他的嵌套属性,除非系统内部临时解除了这个限制。这种机制可以用来冻结传递到组件属性上的对象和处在 mutation 范围外的 Vuex 状态树。
  • 更良好的可调试能力:通过使用新增的 renderTrackedrenderTriggered 钩子,我们可以精确地追踪到一个组件发生重渲染的触发时机和完成时机,及其原因。

<figure>img<figcaption></figcaption></figure>

其他的运行时提升

一句话简介:更小巧,更快速;支持摇树优化;支持 Fragments 和跨组件渲染;支持自定义渲染器。

<summary>展开原文</summary> - Smaller: the new codebase is designed from the ground up to be tree-shaking friendly. Features such as built-in components (, ) and directive runtime helpers (v-model) are now imported on-demand and tree-shakable. The constant baseline size for the new runtime is <10kb gzipped. In addition, features being tree-shakable also allows us to offer more built-in features down the road without incurring payload penalties for users that don’t use them. - Faster: on preliminary benchmarks, we are seeing up to 100% performance improvement across the board, including raw Virtual DOM mounting & patching (we learned quite a few tricks from Inferno, the fastest Virtual DOM implementation out there), component instance initialization and data observation. 3.0 will shave off half the time spent in JavaScript when your app boots up. Fragments & Portals: despite the size reduction, 3.0 comes with built-in support for Fragments (component returning multiple root nodes) and Portals (rendering a sub-tree in another part of the DOM, instead of inside the component). - Improved slots mechanism: All compiler-generated slots are now functions and invoked during the child component’s render call. This ensures dependencies in slots are collected as dependencies for the child instead of the parent. This means that: 1. when slot content changes, only the child re-renders; 2. when the parent re-renders, the child does not have to if its slot content did not change. This change offers even more precise change detection at the component tree level, so even fewer useless re-renders! - Custom Renderer API: a first-class API for creating custom renderers will be available, and no longer requires forking the Vue codebase with custom modifications. This will make it much easier for render-to-native projects like Weex and NativeScript Vue to stay up-to-date with upstream changes. It would also make it trivially easy to create custom renderers for various other purposes.
  • 更小巧:这份新的代码库在设计之初就考虑到了对“摇树优化 (tree-shaking)”的友好。那些如内置组件 (<transition><keep-alive>) 、运行时工具性指令(v-model)等特性将变为按需导入,所以也是“可摇树的”。对于这个新的运行时,它的大小将永远保持在 10kb 之下。另外,使这些特性变为“可摇树的”后,我们就可以提供更多的内置特性,同时还不会增加网络负载——如果没使用到这些特性的话。

    译注:摇树优化,是一种在打包时去除没用到的代码的优化手段,谷歌有一篇教程可以了解下: Reduce JavaScript Payloads with Tree Shaking

  • 更快:在前期的基准测试中,我们看到整体性能有了一倍的提升,包括虚拟DOM的挂载和打补丁(patching,指更新——译注) 的速度(我们从 Inferno 那里学了好些个技巧过来——Inferno 是目前速度最快的虚拟DOM实现),以及组件实例化速度和数据监测的性能。在 3.0 中,你应用的启动时间将缩减一半。

  • 支持 Fragments 和 Portal:虽然体积更小了,但 3.0 还将内置对 Fragments (即允许组件拥有多个根节点) 和 Portal (即允许在 DOM 的其他位置进行渲染,而不是组件内部) 的支持。

    译注:关于 Portal ,你可以将其理解为跨组件渲染或者异地渲染,vue-portal 是一个第三方实现,可以了解一下;Fragments 特性也有一个第三方库,但译者认为这个库的内部实现不够完善,叫做 vue-fragments,感兴趣可以了解一下。

  • 增强的 slot 机制:所有由编译器生成的 slot 都将是函数形式,并且在子组件的 render 函数被调用过程中才被调用 (译注:现在只有 scoped slot 才是函数形式,其渲染的时机也是在父组件的渲染进行时)。这使得 slot 中的依赖项 (即数据——译注) 将被作为子组件的依赖项,而不是现在的父组件;从而意味着:1)当 slot 的内容发生变动时,只有子组件会被重新渲染;2)当父组件重新渲染时,如果子组件的内容未发生变动,子组件就没必要重新渲染。这种机制的改变,可以提供更精确的变动探测,也就可以消除没必要的重渲染。

  • 支持自定义渲染器 (Renderer):这个 API 可以用来创建自定义的渲染器,它将作为“一等公民”出现,到时不再需要 fork 一份 Vue 的代码来通过修改实现自定义。这个 API 的到来,将使得那些如 Weex 和 NativeScript 的“渲染为原生应用”的项目保持与 Vue 的同步更新变得更加容易。除此之外,还将使得那些为了各种用途而创建自定义渲染器变得极其容易。

编译器相关的提升 *

一句话介绍:“摇树友好”的输出;更多的 AOT 优化;更良好的解析错误;支持 source map。

<summary>展开原文</summary> - When targeting tree-shaking-capable bundlers, templates that make use of optional features will generate code that imports those features using ES modules syntax. Unused optional features are thus dropped from the final bundle. - Due to improvements in the new Virtual DOM implementation, we are also able to perform more effective compile-time optimizations such as static tree hoisting, static props hoisting, compiler-hints for runtime to skip children normalization, VNode creation fast paths, etc… - We plan to rewrite the parser to provide location information in template compilation errors. This should also lead to template source map support, and the new parser can serve as the foundation for 3rd party tooling integration, such as eslint-plugin-vue and IDE language services.
  • 如果采用的是支持“摇树优化”的打包器,模板中使用到的那些可选特性,在生成的代码中将通过 ES 的模块语法导入;而在打包后的文件中,那些没用到的可选特性就会被“摇掉”。
  • 由于新的虚拟 DOM 实现所带来的提升,我们可以执行一些更加高效的编译耗时优化,如静态树提升(static tree hoisting)、静态属性提升(static props hoisting);以及为运行时提供一些来自编译器的提示,以此避开子组件的规范过程 (children normalization);提供 VNode 快速创建路径; 等等。
  • 我们计划对解析器进行重写,以便在对模板进行编译发生错误时,可以提供错误发生的位置信息;除此之外还可以带来对模板的 source map 支持;还可以支持第三方工具如 eslint-plugin-vue 和 IDE 的语言服务 (language services) 特性。

兼容 IE 11 *

一句话介绍:IE 11 将受到支持,但将会是另外构建一个版本 (build) 的形式支持,不过这个版本会存在与 Vue 2.x 响应式机制所存在的同样的局限。

<summary>展开原文</summary> The new codebase currently targets evergreen browsers only and assumes baseline native ES2015 support. But alas, we know a lot of our users still need to support IE11 for the foreseeable future. Most of the ES2015 features used can be transpiled / polyfilled for IE11, with the exception for Proxies. Our plan is to implement an alternative observer with the same API, but using the good old ES5 Object.defineProperty API. A separate build of Vue 3.x will be distributed using this observer implementation. However, this build will be subject to the same change detection caveats of Vue 2.x and thus not fully compatible with the “modern” build of 3.x. We are aware that this imposes some inconvenience for library authors as they will need to be aware of compatibility for two different builds, but we will make sure to provide clear guidelines on this when we reach that stage.

新的代码库目前只针对主流浏览器,而且我们假定他们都支持 ES2015。但是,哎,我们也知道在可预见的未来还有很多用户仍然需要支持 IE11。除了 Proxy 外,大多数 ES2015 的特性都可以用转译或者垫片的方式在 IE11 中使用。我们的计划是另外单独实现一个具有同样 API 的替代性 observer,不过是基于老式的 Object.defineProperty API;然后再通过单独构建一个使用这个实现的 Vue 3.x 版本 (build) 进行发布,不过这个单独的版本还是会有 Vue 2.x 在变动探测方面所存在的问题,所以它其实并不是一个完全兼容 3.x 的一个版本。我们也意识到这会给第三方库的作者们带来某些不便,因为他们需要考虑两个不同版本之间的兼容性问题,不过当我们真的推进到那个阶段时,那时我们肯定会确保提供一份清晰的指导 (关于如何处理这个问题的指导——译注) 。

我们将如何达成目标

虽然我们是在今天宣布的,不过我们还没有一个确定的时间表,目前我们有的是实现这些目标的步骤:

1. 征集运行时原型的反馈

<summary>展开原文</summary> This is the phase we are in right now. Currently, we already have a working runtime prototype that includes the new observer, Virtual DOM and component implementation. We have invited a group of authors of influential community projects to provide feedback for the internal changes, and would like to make sure they are comfortable with the changes before moving forward. We want to ensure that important libraries in the ecosystem will be ready at the same time when we release 3.0, so that users relying on those projects can upgrade easily.

这也是我们当前所处的阶段。目前,我们已经有了一个能够运行的运行时原型,它包括一个新的 observer、新的虚拟 DOM和一个新的组件实现。我们邀请了一队流行的社区项目的作者,收集他们对这些底层变动的反馈,希望在继续推进前他们对这些变动能够轻松适应。我们希望在 3.0 发布之时,Vue 生态中的这些重点的三方库也已经同步做好了准备,以便依赖于这些项目的用户可以轻松地升级。

2. 通过 RFC 征集公众反馈

<summary>展开原文</summary> Once we gain a certain level of confidence in the new design, for each breaking change we will be opening a dedicated RFC issue which includes:

Scope of the change;

  • Reasoning behind the change: what do we gain, and what tradeoffs are being made;
  • Upgrade path: can it be introduced in a completely backwards-compatible fashion, via a removable compatibility layer, or via codemods?
  • We will anticipate public feedback from the wider community to help us consolidate these ideas.

在我们对这份新的设计有了某种程度的信心之后,我们会为每一项非兼容性变动设立一个专门的 RFC 频道,主要将包含以下信息:

  • 该项变动的影响范围;
  • 该项变动的得失考量:我们会得到什么,又有哪些代价。
  • 该项变动的升级途径:是采用完全后向兼容的形式,还是通过植入一个可移除的兼容性层,或者是通过修改代码来升级?

3. 在 2.x 和 2.x-next 中引入兼容性特性

<summary>展开原文</summary> We are not forgetting about 2.x! In fact, we plan to use 2.x to progressively accustom users to the new changes. We will be gradually introducing confirmed API changes into 2.x via opt-in adaptors, and 2.x-next will allow users to try out the new Proxy-based observer.

The last minor release in 2.x will become LTS and continue to receive bug and security fixes for 18 months when 3.0 is released.

我们不会忘记 2.x!我们计划通过 2.x 来让用户渐进式地适应这些新的变动。我们会通过一些适配器逐步地往 2.x 中引入验证过得 API 变动;另外,2.x-next 版本还将允许用户尝试新的基于 Proxy 的 observer。

最后一次发布的 2.x 的次版本将成为 LTS 版本,在 3.0 发布后的 18 个月内将继续接收到 bug 和 安全性修复。

4. Alpha 阶段

<summary>展开原文</summary> Next, we will finish up the compiler and server-side rendering parts of 3.0 and start making alpha releases. These will mostly be for stability testing purposes in small greenfield apps.

在接下来的这个阶段,我们将完成 3.0 的编译器和服务端渲染的部分,并开始制作 alpha 版本。这些工作的主要目的是为了在一些小的应用中进行稳定性测试。

5. Beta 阶段

<summary>展开原文</summary> During beta phase, our main goal is updating support libraries and tools like Vue Router, Vuex, Vue CLI, Vue DevTools and make sure they work smoothly with the new core. We will also be working with major library authors from the community to help them get ready for 3.0.

在 beta 阶段,我们的主要目标是更新相关的支持库,如 Vue Router、Vuex、Vue CLI、Vue DevTools,以此确保他们能够流畅地与这个新的内核协同。另外我们还会通过社区来帮助第三方库的开发者们,与他们一起工作,迎接 3.0 的到来。

6. RC 阶段

<summary>展开原文</summary> Once we consider the API and codebase stable, we will enter RC phase with API freeze. During this phase we will also work on a “compat build”: a build of 3.0 that includes compatibility layers for 2.x API. This build will also ship with a flag you can turn on to emit deprecation warnings for 2.x API usage in your app. The compat build can be used as a guide to upgrade your app to 3.0.

当我们认为各项 API 和代码库已经稳定时,我们将进入 RC 阶段,同时 API 也就固定下来了。在这个阶段,我们还将构建一个“兼容版本”(compat build) :一种包含了兼容 2.x API 的兼容性层的 3.0 版本,它还会提供一个标记,你可以打开这个标记,以此让其在你应用使用了 2.x API 的地方发出 API 已经过时的警告提示;因此这个“兼容版本”也可以用来在升级 3.0 时提供指南 (即给出那些地方需要升级——译注)。

7. 构建 IE 11 版本

The last task before the final release will be the IE11 compatibility build as mentioned above.

最终发布前的最后一项任务就是前面提到的那个兼容 IE 11 的版本。

8. 最终发布

<summary>展开原文</summary> In all honesty, we don’t know when this will happen yet, but likely in 2019. Again, we care more about shipping something that is solid and stable rather than hitting specific dates. There is a lot of work to be done, but we are excited for what’s coming next!

坦率讲,我们还不知道何时能推进到这个阶段,不过可能是在 2019 年。这又一次表明,我们追求的是稳固性而不是具体的某个日期。虽然工作量很大,但我们对于新到来的这些特性还是非常激动!

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