vue-debug-guides

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