diff --git a/src/api/directives.md b/src/api/directives.md index 06f9bd23a..a5218a11c 100644 --- a/src/api/directives.md +++ b/src/api/directives.md @@ -466,21 +466,19 @@ ``` - - Since 3.2, you can also memoize part of the template with invalidation conditions using [`v-memo`](#v-memo). + 自 3.2 开始,你还可以通过 [`v-memo`](#v-memo) 来记住带有失效条件的部分模板。 - **参考**: - [数据绑定语法- 插值](../guide/template-syntax.html#文本) - [v-memo](#v-memo) - ## v-memo -- **Expects:** `Array` +- **预期** `Array` -- **Details:** +- **详细** - Memoize a sub-tree of the template. Can be used on both elements and components. The directive expects a fixed-length array of dependency values to compare for the memoization. If every value in the array was the same as last render, then updates for the entire sub-tree will be skipped. For example: + 对模板的一个子树进行记忆。在元素和组件上均可以使用。该指令通过一个固定长度的依赖数组来进行记忆比较。如果数组中的每个值跟最后一次渲染时相比都没有发生变化,那么整个子树的更新都将被跳过。举例: ```html
@@ -488,13 +486,13 @@
``` - When the component re-renders, if both `valueA` and `valueB` remain the same, all updates for this `
` and its children will be skipped. In fact, even the Virtual DOM VNode creation will also be skipped since the memoized copy of the sub-tree can be reused. + 当组件重新渲染的时候,如果 `valueA` 与 `valueB` 都维持不变,那么对这个 `
` 以及它的所有子节点的更新都将被跳过。事实上,即使是虚拟 DOM 的 VNode 创建也将被跳过,因为子树的记忆副本可以被重用。 - It is important to specify the memoization array correctly, otherwise we may skip updates that should indeed be applied. `v-memo` with an empty dependency array (`v-memo="[]"`) would be functionally equivalent to `v-once`. + 正确地声明记忆数组是很重要的,否则某些事实上需要被应用的更新也可能会被跳过。带有空依赖数组的 `v-memo` (`v-memo="[]"`) 在功能上等效于 `v-once`。 - **Usage with `v-for`** + **结合 `v-for` 使用** - `v-memo` is provided solely for micro optimizations in performance-critical scenarios and should be rarely needed. The most common case where this may prove helpful is when rendering large `v-for` lists (where `length > 1000`): + `v-memo` 仅仅是为了在某些性能非常关键的场景下提供一些微观的优化,它应该很少需要被用到。最常见的能够证明其价值的场景是渲染大型的 `v-for` 列表 (比如 `length > 1000`): ```html
@@ -503,16 +501,17 @@
``` - When the component's `selected` state changes, a large amount of VNodes will be created even though most of the items remained exactly the same. The `v-memo` usage here is essentially saying "only update this item if it went from non-selected to selected, or the other way around". This allows every unaffected item to reuse its previous VNode and skip diffing entirely. Note we don't need to include `item.id` in the memo dependency array here since Vue automatically infers it from the item's `:key`. + 当组件的 `selected` 状态发生变化时,即使绝大多数 item 都没有发生任何变化,大量的 VNode 仍将被创建。此处使用的 `v-memo` 本质上代表着“仅在 item 从未选中变为选中时更新它,反之亦然”。这允许每个未受影响的 item 重用之前的 VNode,并完全跳过差异比较。注意,我们不需要把 `item.id` 包含在记忆依赖数组里面,因为 Vue 可以自动从 item 的 `:key` 中把它推断出来。 :::warning - When using `v-memo` with `v-for`, make sure they are used on the same element. **`v-memo` does not work inside `v-for`.** + 在 `v-for` 中使用 `v-memo` 时,确保它们被用在了同一个元素上。 **`v-memo` 在 `v-for` 内部是无效的。** ::: - `v-memo` can also be used on components to manually prevent unwanted updates in certain edge cases where the child component update check has been de-optimized. But again, it is the developer's responsibility to specify correct dependency arrays to avoid skipping necessary updates. + `v-memo` 也可以用于组件,在子组件的更新检查未进行优化的某些极端场景下,手动防止不必要的更新。但是,重申一遍,开发者有责任指定正确的依赖数组,以避免必要的更新被跳过。 -- **See also:** +- **参考:** - [v-once](#v-once) + ## v-is -已在 3.1.0 中被废弃。请换用[带有 `vue` 前缀的 `is` attribute](/api/special-attributes.html#is)。 +已在 3.1.0 中被废弃。请换用[带有 `vue:` 前缀的 `is` attribute](/api/special-attributes.html#is)。