Vue 3 debugging and error handling for runtime issues, warnings, async failures, and hydration bugs. For development best practices and common gotchas, use vue-best-practices .

Reactivity

• Tracing unexpected re-renders and state updates → See reactivity-debugging-hooks

• Ref values not updating due to missing .value access → See ref-value-access

• State stops updating after destructuring reactive objects → See reactive-destructuring

• Refs inside arrays, Maps, or Sets not unwrapping → See refs-in-collections-need-value

• Nested refs rendering as [object Object] in templates → See template-ref-unwrapping-top-level

• Reactive proxy identity comparisons always return false → See reactivity-proxy-identity-hazard

• Third-party instances breaking when proxied → See reactivity-markraw-for-non-reactive

• Watchers only firing once per tick unexpectedly → See reactivity-same-tick-batching

Computed

• Computed getter triggers mutations or requests unexpectedly → See computed-no-side-effects

• Mutating computed values causes changes to disappear → See computed-return-value-readonly

• Computed value never updates after conditional logic → See computed-conditional-dependencies

• Sorting or reversing arrays breaks original state → See computed-array-mutation

• Passing parameters to computed properties fails → See computed-no-parameters

Watchers

• Async operations overwriting with stale data → See watch-async-cleanup

• Creating watchers inside async callbacks → See watch-async-creation-memory-leak

• Watcher never triggers for reactive object properties → See watch-reactive-property-getter

• Async watchEffect misses dependencies after await → See watcheffect-async-dependency-tracking

• DOM reads are stale inside watcher callbacks → See watch-flush-timing

• Deep watchers report identical old/new values → See watch-deep-same-object-reference

• watchEffect runs before template refs update → See watcheffect-flush-post-for-refs

Components

• Child component throws "component not found" error → See local-components-not-in-descendants

• Click listener doesn't fire on custom component → See click-events-on-components

• Parent can't access child ref data in script setup → See component-ref-requires-defineexpose

• HTML template parsing breaks Vue component syntax → See in-dom-template-parsing-caveats

• Wrong component renders due to naming collisions → See component-naming-conflicts

• Parent styles don't apply to multi-root component → See multi-root-component-class-attrs

Props & Emits

• Variables referenced in defineProps cause errors → See prop-defineprops-scope-limitation

• Component emits undeclared event causing warnings → See declare-emits-for-documentation

• defineEmits used inside function or conditional → See defineEmits-must-be-top-level

• defineEmits has both type and runtime arguments → See defineEmits-no-runtime-and-type-mixed

• Native event listeners not responding to clicks → See native-event-collision-with-emits

• Component event fires twice when clicking → See undeclared-emits-double-firing

Templates

• Getting template compilation errors with statements → See template-expressions-restrictions

• "Cannot read property of undefined" runtime errors → See v-if-null-check-order

• Dynamic directive arguments not working properly → See dynamic-argument-constraints

• v-else elements rendering unconditionally always → See v-else-must-follow-v-if

• Mixing v-if with v-for causes precedence bugs and migration breakage → See no-v-if-with-v-for

• Template function calls mutating state cause unpredictable re-render bugs → See template-functions-no-side-effects

• Child components in loops showing undefined data → See v-for-component-props

• Array order changing after sorting or reversing → See v-for-computed-reverse-sort

• List items disappearing or swapping state unexpectedly → See v-for-key-attribute

• Getting off-by-one errors with range iteration → See v-for-range-starts-at-one

• v-show or v-else not working on template elements → See v-show-template-limitation

Template Refs

• Ref becomes null when element is conditionally hidden → See template-ref-null-with-v-if

• Ref array indices don't match data array in loops → See template-ref-v-for-order

• Refactoring template ref names breaks silently in code → See use-template-ref-vue35

Forms & v-model

• Initial form values not showing when using v-model → See v-model-ignores-html-attributes

• Textarea content changes not updating the ref → See textarea-no-interpolation

• iOS users cannot select dropdown first option → See select-initial-value-ios-bug

• Parent and child components have different values → See define-model-default-value-sync

• Object property changes not syncing to parent → See definemodel-object-mutation-no-emit

• Real-time search/validation broken for Chinese/Japanese input → See v-model-ime-composition

• Number input returns empty string instead of zero → See v-model-number-modifier-behavior

• Custom checkbox values not submitted in forms → See checkbox-true-false-value-form-submission

Events & Modifiers

• Chaining multiple event modifiers produces unexpected results → See event-modifier-order-matters

• Keyboard shortcuts don't fire with system modifier keys → See keyup-modifier-timing

• Keyboard shortcuts fire with unintended modifier combinations → See exact-modifier-for-precise-shortcuts

• Combining passive and prevent modifiers breaks event behavior → See no-passive-with-prevent

Lifecycle

• Memory leaks from unremoved event listeners → See cleanup-side-effects

• DOM access fails before component mounts → See lifecycle-dom-access-timing

• DOM reads return stale values after state changes → See dom-update-timing-nexttick

• SSR rendering differs from client hydration → See lifecycle-ssr-awareness

• Lifecycle hooks registered asynchronously never run → See lifecycle-hooks-synchronous-registration

Slots

• Accessing child component data in slot content returns undefined values → See slot-render-scope-parent-only

• Mixing named and scoped slots together causes compilation errors → See slot-named-scoped-explicit-default

• Using v-slot on native HTML elements causes compilation errors → See slot-v-slot-on-components-or-templates-only

• Unexpected content placement from implicit default slot behavior → See slot-implicit-default-content

• Scoped slot props missing expected name property → See slot-name-reserved-prop

• Wrapper components breaking child slot functionality → See slot-forwarding-to-child-components

Provide/Inject

• Calling provide after async operations fails silently → See provide-inject-synchronous-setup

• Tracing where provided values come from → See provide-inject-debugging-challenges

• Injected values not updating when provider changes → See provide-inject-reactivity-not-automatic

• Multiple components share same default object → See provide-inject-default-value-factory

Attrs

• Both internal and fallthrough event handlers execute → See attrs-event-listener-merging

• Explicit attributes overwritten by fallthrough values → See fallthrough-attrs-overwrite-vue3

• Attributes applying to wrong element in wrappers → See inheritattrs-false-for-wrapper-components

Composables

• Composable called outside setup context or asynchronously → See composable-call-location-restrictions

• Composable reactive dependency not updating when input changes → See composable-tovalue-inside-watcheffect

• Composable mutates external state unexpectedly → See composable-avoid-hidden-side-effects

• Destructuring composable returns breaks reactivity unexpectedly → See composable-naming-return-pattern

Composition API

• Lifecycle hooks failing silently after async operations → See composition-api-script-setup-async-context

• Parent component refs unable to access exposed properties → See define-expose-before-await

• Functional-programming patterns break expected Vue reactivity behavior → See composition-api-not-functional-programming

• React Hook mental model causes incorrect Composition API usage → See composition-api-vs-react-hooks-differences

Animation

• Animations fail to trigger when DOM nodes are reused → See animation-key-for-rerender

• TransitionGroup list updates feel laggy under load → See animation-transitiongroup-performance

TypeScript

• Mutable prop defaults leak state between component instances → See ts-withdefaults-mutable-factory-function

• reactive() generic typing causes ref unwrapping mismatches → See ts-reactive-no-generic-argument

• Template refs throw null access errors before mount or after v-if unmount → See ts-template-ref-null-handling

• Optional boolean props behave as false instead of undefined → See ts-defineprops-boolean-default-false

• Imported defineProps types fail with unresolvable or complex type references → See ts-defineprops-imported-types-limitations

• Untyped DOM event handlers fail under strict TypeScript settings → See ts-event-handler-explicit-typing

• Dynamic component refs trigger reactive component warnings → See ts-shallowref-for-dynamic-components

• Union-typed template expressions fail type checks without narrowing → See ts-template-type-casting

Async Components

• Route components misconfigured with defineAsyncComponent lazy loading → See async-component-vue-router

• Network failures or timeouts loading components → See async-component-error-handling

• Template refs undefined after component reactivation → See async-component-keepalive-ref-issue

Render Functions

• Render function output stays static after state changes → See rendering-render-function-return-from-setup

• Reused vnode instances render incorrectly → See render-function-vnodes-must-be-unique

• String component names render as HTML elements → See rendering-resolve-component-for-string-names

• Accessing vnode internals breaks on Vue updates → See render-function-avoid-internal-vnode-properties

• Vue 2 render function patterns crash in Vue 3 → See rendering-render-function-h-import-vue3

• Slot content not rendering from h() → See rendering-render-function-slots-as-functions

KeepAlive

• Child components mount twice with nested Vue Router routes → See keepalive-router-nested-double-mount

• Memory grows when combining KeepAlive with Transition animations → See keepalive-transition-memory-leak

Transitions

• JavaScript transition hooks hang without done callback → See transition-js-hooks-done-callback

• Move animations fail on inline list elements → See transition-group-flip-inline-elements

• List items jump instead of smoothly animating → See transition-group-move-animation-position-absolute

• Vue 2 to Vue 3 TransitionGroup wrapper changes break layout → See transition-group-no-default-wrapper-vue3

• Nested transitions cut off before finishing → See transition-nested-duration

• Scoped styles stop working in reusable transition wrappers → See transition-reusable-scoped-style

• RouterView transitions animate unexpectedly on first render → See transition-router-view-appear

• Mixing CSS transitions and animations causes timing issues → See transition-type-when-mixed

• Cleanup hooks missed during rapid transition swaps → See transition-unmount-hook-timing

Teleport

• Teleport target element not found in DOM → See teleport-target-must-exist

• Teleported content breaks SSR hydration → See teleport-ssr-hydration

• Scoped styles not applying to teleported content → See teleport-scoped-styles-limitation

Suspense

• Need to handle async errors from Suspense components → See suspense-no-builtin-error-handling

• Using Suspense with server-side rendering → See suspense-ssr-hydration-issues

• Async component loading/error UI ignored under Suspense → See async-component-suspense-control

SSR

• HTML differs between server and client renders → See ssr-hydration-mismatch-causes

• User state leaks between requests from shared singleton stores → See state-ssr-cross-request-pollution

• Browser-only APIs crash server rendering in universal code paths → See ssr-platform-specific-apis

Performance

• List children re-render unnecessarily because parent passes unstable props → See perf-props-stability-update-optimization

• Computed objects retrigger effects despite equivalent values → See perf-computed-object-stability

SFC (Single File Components)

• Trying to use named exports from component script blocks → See sfc-named-exports-forbidden

• Variables not updating in template after changes → See sfc-script-setup-reactivity

• Scoped styles not applying to child component elements → See sfc-scoped-css-child-component-styling

• Scoped styles not applying to dynamic v-html content → See sfc-scoped-css-dynamic-content

• Scoped styles not applying to slot content → See sfc-scoped-css-slot-content

• Tailwind classes missing when built dynamically → See tailwind-dynamic-class-generation

• Recursive components not rendering due to name conflicts → See self-referencing-component-name

Plugins

• Debugging why global properties cause naming conflicts → See plugin-global-properties-sparingly

• Plugin not working or inject returns undefined → See plugin-install-before-mount

• Plugin global properties are unavailable in setup-based components → See plugin-prefer-provide-inject-over-global-properties

• Plugin type augmentation mistakes break ComponentCustomProperties typing → See plugin-typescript-type-augmentation

App Configuration

• App configuration methods not working after mount call → See configure-app-before-mount

• Chaining app config off mount() fails because mount returns component instance → See mount-return-value

• require.context-based component auto-registration fails in Vite → See dynamic-component-registration-vite