v2.7.0

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Backported Features

• Composition API
• SFC <script setup>
• SFC CSS v-bind

In addition, the following APIs are also supported:

• defineComponent() with improved type inference (compared to Vue.extend)

• h(), useSlot(), useAttrs(), useCssModules()

• set(), del() and nextTick() are also provided as named exports in ESM builds.

• The emits option is also supported, but only for type-checking purposes (does not affect runtime behavior)

  2.7 also supports using ESNext syntax in template expressions. When using a build system, the compiled template render function will go through the same loaders / plugins configured for normal JavaScript. This means if you have configured Babel for .js files, it will also apply to the expressions in your SFC templates.

Notes on API exposure

• In ESM builds, these APIs are provided as named exports (and named exports only):

  import Vue, { ref } from 'vue'
  
  Vue.ref // undefined, use named export instead

• In UMD and CJS builds, these APIs are exposed as properties on the global Vue object.

• When bundling with CJS builds externalized, bundlers should be able to handle ESM interop when externalizing CJS builds.

Behavior Differences from Vue 3

The Composition API is backported using Vue 2's getter/setter-based reactivity system to ensure browser compatibility. This means there are some important behavior differences from Vue 3's proxy-based system:

• All Vue 2 change detection caveats still apply.

• reactive(), ref(), and shallowReactive() will directly convert original objects instead of creating proxies. This means:

  // true in 2.7, false in 3.x
  reactive(foo) === foo

• readonly() does create a separate object, but it won't track newly added properties and does not work on arrays.

• Avoid using arrays as root values in reactive() because without property access the array's mutation won't be tracked (this will result in a warning).

• Reactivity APIs ignore properties with symbol keys.

In addition, the following features are explicitly NOT ported:

• ❌ createApp() (Vue 2 doesn't have isolated app scope)
• ❌ Top-level await in <script setup> (Vue 2 does not support async component initialization)
• ❌ TypeScript syntax in template expressions (incompatible w/ Vue 2 parser)
• ❌ Reactivity transform (still experimental)
• ❌ expose option is not supported for options components (but defineExpose() is supported in <script setup>).

Upgrade Guide

Vue CLI / webpack

1. Upgrade local @vue/cli-xxx dependencies the latest version in your major version range (if applicable):

   • ~4.5.18 for v4
   • ~5.0.6 for v5

2. Upgrade vue to ^2.7.0. You can also remove vue-template-compiler from the dependencies - it is no longer needed in 2.7.

   Note: if you are using @vue/test-utils, you may need to keep it in the dependencies for now, but this requirement will also be lifted in a new release of test utils.

3. Check your package manager lockfile to ensure the following dependencies meet the version requirements. They may be transitive dependencies not listed in package.json.

   • vue-loader: ^15.10.0
   • vue-demi: ^0.13.1

   If not, you will need to remove node_modules and the lockfile and perform a fresh install to ensure they are bumped to the latest version.

4. If you were previously using @vue/composition-api, update imports from it to vue instead. Note that some APIs exported by the plugin, e.g. createApp, are not ported in 2.7.

5. Update eslint-plugin-vue to latest version (9+) if you run into unused variable lint errors when using <script setup>.

6. The SFC compiler for 2.7 now uses PostCSS 8 (upgraded from 7). PostCSS 8 should be backwards compatible with most plugins, but the upgrade may cause issues if you were previously using a custom PostCSS plugin that can only work with PostCSS 7. In such cases, you will need to upgrade the relevant plugins to their PostCSS 8 compatible versions.

Vite

2.7 support for Vite is provided via a new plugin: @​vitejs/plugin-vue2. This new plugin requires Vue 2.7 or above and supersedes the existing vite-plugin-vue2.

Note that the new plugin does not handle Vue-specific JSX / TSX transform, which is intentional. Vue 2 JSX / TSX transform should be handled in a separate, dedicated plugin, which will be provided soon.

Volar Compatibility

2.7 ships improved type definitions so it is no longer necessary to install @vue/runtime-dom just for Volar template type inference support. All you need now is the following config in tsconfig.json:

{
  // ...
  "vueCompilerOptions": {
    "target": 2.7
  }
}

Devtools Support

Vue Devtools 6.2.0 has added support for inspecting 2.7 Composition API state, but the extensions may still need a few days to go through review on respective publishing platforms.

Bug Fixes

• sfc: only include legacy decorator parser plugin when new plugin is not used (326d24a)