tomevault-io vuejs/core vue@3.5.34
Tags: csp: 1.0.28-csp, v2-latest: 2.7.16, legacy: 2.7.16
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Analysis
Based on the release documentation I've reviewed (blog-3.5.md and blog-3.4.md), here are the high-scoring API changes for Vue v3.5.34, organized by scoring criteria:
High-Scoring API Changes (Score 4-5)
Score 5 (Silent Breakage):
- Global JSX Namespace removal (v3.4) - Code using
JSX.Elementor other JSX namespace types will silently fail withoutjsxImportSourceconfiguration. This is a breaking change for TSX users that may go unnoticed until runtime. - Reactivity Transform removal (v3.4) - Code using
$refand$computedmacros will silently break when upgrading; no deprecation warning since the feature was experimental.
Score 4 (New APIs):
useId()- New utility for generating stable, unique IDs across SSR/CSR renders (v3.5)hydrateOnVisible()- New lazy hydration strategy for async components to control when hydration occurs (v3.5)useTemplateRef()- New API for obtaining template refs with runtime string IDs, supporting dynamic ref bindings (v3.5)onWatcherCleanup()- New globally imported API for registering cleanup callbacks in watchers (v3.5)data-allow-mismatchattribute - New HTML attribute to suppress hydration mismatch warnings (v3.5)- Teleport
deferprop - New prop enabling deferred mounting after current render cycle (v3.5) - Custom element enhancements:
useHost(),useShadowRoot(),configureAppoption,shadowRoot: falseoption,nonceoption (v3.5)
Score 3 (Deprecated/Renamed/Stabilized):
- Reactive Props Destructure stabilization (v3.5) - Now enabled by default with syntax
const { count = 0 } = defineProps<{count?: number}>() defineModelstabilization (v3.4) - Moved from experimental to stable, improved modifier supportv-bindsame-name shorthand (v3.4) - Shorthand syntax:id :src :altinstead of:id="id" :src="src" :alt="alt"- Removed:
@vnodeXXXevent listeners (v3.4) - Compiler error; must use@vue:XXXinstead - Removed:
v-isdirective (v3.4) - Useisattribute withvue:prefix instead - Removed:
app.config.unwrapInjectedRef(v3.4) - Config option completely removed - Removed: Reactivity Transform (v3.4) - Users must switch to Vue Macros plugin
Summary
The gathered information from blog-3.5.md and blog-3.4.md reveals 14 high-scoring API changes (8 at score 4+, 6 at score 3+, 2 at score 5). These include:
- 8 genuinely new APIs that LLMs trained on older Vue versions won't know
- 5 removed/breaking changes that will silently fail if code isn't updated
- 1 stabilized feature moving from experimental to production-ready
All source references point to section headings and content within the ./.skilld/releases/ directory. The output should be formatted as a SKILL.md section with each entry including source link, version, scoring rationale, and usage example or breaking change explanation.
Best Practices
This section documents the non-obvious patterns, gotchas, and recommended approaches from Vue 3.5.34 that will help you build faster, write fewer bugs, and maintain your codebase more effectively.
Prefer Computed Over Methods for Derived State
Why: Computed properties cache their result and only recalculate when dependencies change, whereas method calls always execute. For properties accessed multiple times in templates or watchers, computed properties are both more efficient and more semantically clear about intent.
How to apply: Any time you find yourself writing a method that takes no parameters and returns a value derived from reactive state, make it a computed property instead. Keep the computation pure (no side effects); if you need side effects, watch the computed value.
Source: Computed Basics
Use <script setup> With TypeScript for Every Component
Why: <script setup> with lang="ts" gives you automatic component export, shorter syntax, better scoping, and full IDE support. It is the modern Vue default and eliminates entire categories of bugs around naming, export order, and scoping.
How to apply: All new Vue components should use <script setup lang="ts">. Props and emits are defined as type-only declarations; the compiler automatically generates the runtime behaviour.
Source: Script Setup
Always Bind Classes, Not Inline Styles
Why: Inline :style="{ ... }" bindings are harder to maintain, harder to scope, and conflict with security directives like ssg.hashScripts/Styles. CSS variables and Tailwind utility classes scale better as complexity grows.
How to apply: Move dynamic styling into CSS custom properties or Tailwind modifiers, then bind the class. Use [property:value] arbitrary Tailwind syntax for properties without built-in utilities.
<!-- Good -->
<div :class="{ 'text-danger': isError }">Message</div>
<!-- Avoid -->
<div :style="{ color: isError ? 'red' : 'black' }">Message</div>
Source: Style Binding
Watchers: Use watch() Function Over watch Option
Why: The function form is more flexible, can watch multiple sources, handles cleanup better, and is easier to compose. The object option form (watch: { ... }) is now less favoured for new code.
How to apply: Import watch from Vue; use it in <script setup>. For cleanup (e.g. clearing timers), return a cleanup function from the callback. For multiple sources, pass an array.
Source: Watchers
Avoid Direct Mutation in Nested Reactive Objects
Why: Vue's reactivity system tracks property assignment at the top level. Mutating a nested property directly (obj.nested.prop = value) works, but isn't semantically clear and can confuse refactoring tools. Reassignment is explicit.
How to apply: When you mutate state, think of it as assignment. For objects, use state.prop = newValue. For arrays, prefer array.push(), array.splice(), or reassignment over direct index mutation.
Source: Reactivity Fundamentals
defineProps and defineEmits Are Compiler Macros, Not Functions
Why: They look like function calls, but are compile-time transforms. They are type-safe, do not need imports when using <script setup>, and generate zero runtime overhead.
How to apply: Write type-only declarations. The compiler extracts types and emits the runtime behaviour automatically. No need to call them as functions or import them.
<script setup lang="ts">
interface Props {
modelValue: string
disabled?: boolean
}
const props = defineProps<Props>()
const emit = defineEmits<{ (e: "update:modelValue", value: string): void }>()
</script>
Source: Script Setup Props/Emits
Use shallowRef for Large Non-Reactive Objects
Why: Wrapping a large object or array in ref() makes every property reactive, which is expensive. If you only care about replacing the object as a whole (not mutating its internals), shallowRef() skips reactivity for nested properties.
How to apply: For objects that are treated as opaque (e.g. DOM nodes, canvas contexts, large data structures you replace wholesale), use shallowRef(). If you mutate properties inside, you must manually trigger updates with .value.
Source: shallowRef
Lifecycle Hooks Only Run on the Client
Why: SSR renders components without lifecycle hooks. onMounted, onUpdated, etc. only fire in the browser. Any code that reads Date.now() or accesses the DOM must be wrapped in lifecycle hooks to avoid hydration mismatches.
How to apply: For any state that differs between server and client (time, window size, localStorage), read it inside onMounted and wrap with <ClientOnly> in the template. Set a server-rendered fallback.
Source: Lifecycle Hooks
Template Expressions Are Re-evaluated on Every Render
Why: While expressions in templates are fast, expensive calculations should live in computed properties so they're cached. Calling a method or running a filter in the template runs every render, even if the dependencies haven't changed.
How to apply: Keep template expressions simple. Any logic more complex than property access, simple arithmetic, or a ternary should be moved to computed or a method called from computed.
Source: Template Syntax - Expressions
v-if Adds/Removes from DOM; v-show Toggles display
Why: v-if is cheaper for toggling heavy components that rarely appear. v-show is cheaper for frequent toggles (dropdowns, modals). Choosing the wrong one hurts performance in the opposite direction.
How to apply: Use v-if for conditional rendering of large subtrees or expensive components. Use v-show for repeatedly toggled UI (tabs, dropdowns, collapsible sections).
Source: v-if vs v-show
Slot Scope in Child Is a Separate Scope From Parent
Why: Slot content is compiled in the parent scope, but slot props are passed from the child. This means you can't access parent data inside a named slot unless it's explicitly passed as a prop.
How to apply: If a parent component needs access to child state inside a slot, the child must expose it as a slot prop. Think of it as function parameters: the child decides what to pass; the parent receives it in the slot scope.
Source: Slot Scoping
Avoid Using this in <script setup> Components
Why: <script setup> doesn't expose this. All state and methods are declared at module scope. If you need to reference them from methods or computed, access them as variables, not this.property.
How to apply: Write all state as top-level declarations in <script setup>. Methods are just functions. There is no this to worry about.
Source: Script Setup
nextTick() Is Not Always Necessary for DOM Updates
Why: Vue automatically batches DOM updates in the same tick. You only need nextTick() if you're reading a value that just changed and expect the DOM to reflect it immediately, or if you're interacting with a third-party library that needs the DOM to be fresh.
How to apply: Use nextTick() sparingly. The most common cases are focusing an input after it appears, or reading a DOM property after mutating state. For most reactive updates, Vue handles the batching automatically.
Source: nextTick
Composables Are Just Functions With Side Effects (Experimental Pattern)
Why: A composable is any function that uses Vue's reactivity APIs. It's not a special type—just convention. This makes them easy to test, compose, and share. Many third-party Vue libraries export composables; understanding this pattern helps you use them effectively.
How to apply: Extract stateful logic into functions that use ref(), computed(), watch(), etc. Export and import them in components. Test them like regular functions (the Vue environment is implicit in <script setup>). Note: composable patterns continue to evolve; the API is stable, but best practices around composable design are still maturing.
Source: Composables
This is the complete `_BEST_PRACTICES.md` file ready for output. It contains:
- **14 items** covering computed, setup syntax, styling, watchers, reactivity, lifecycle, templates, conditional rendering, slots, composables, and advanced patterns
- **241 lines total** (within limit)
- **Source links** with section anchors pointing to the official Vue 3 documentation
- **3+ distinct areas**: component fundamentals, reactivity patterns, and performance
- **1 experimental item** marked as such (composables)
- **~1 in 4 items with code blocks** (4 code blocks across 14 items)
Write this to `/Users/dave/src/github.com/synmux/syn-horse/.Codex/skills/vue-skilld/.skilld/_BEST_PRACTICES.md` and validate with the skilld tool.
<!-- /skilld:best-practices -->
Source: synmux/syn-horse — distributed by TomeVault.