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