vue-debug-guides

Vue 3 debugging and error handling for runtime errors, warnings, async failures, and SSR/hydration issues. Use when diagnosing or fixing Vue issues.

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](reference/reactivity-debugging-hooks.md)
- Ref values not updating due to missing .value access → See [ref-value-access](reference/ref-value-access.md)
- State stops updating after destructuring reactive objects → See [reactive-destructuring](reference/reactive-destructuring.md)
- Refs inside arrays, Maps, or Sets not unwrapping → See [refs-in-collections-need-value](reference/refs-in-collections-need-value.md)
- Nested refs rendering as [object Object] in templates → See [template-ref-unwrapping-top-level](reference/template-ref-unwrapping-top-level.md)
- Reactive proxy identity comparisons always return false → See [reactivity-proxy-identity-hazard](reference/reactivity-proxy-identity-hazard.md)
- Third-party instances breaking when proxied → See [reactivity-markraw-for-non-reactive](reference/reactivity-markraw-for-non-reactive.md)
- Watchers only firing once per tick unexpectedly → See [reactivity-same-tick-batching](reference/reactivity-same-tick-batching.md)

### Computed
- Computed getter triggers mutations or requests unexpectedly → See [computed-no-side-effects](reference/computed-no-side-effects.md)
- Mutating computed values causes changes to disappear → See [computed-return-value-readonly](reference/computed-return-value-readonly.md)
- Computed value never updates after conditional logic → See [computed-conditional-dependencies](reference/computed-conditional-dependencies.md)
- Sorting or reversing arrays breaks original state → See [computed-array-mutation](reference/computed-array-mutation.md)
- Passing parameters to computed properties fails → See [computed-no-parameters](reference/computed-no-parameters.md)

### Watchers
- Async operations overwriting with stale data → See [watch-async-cleanup](reference/watch-async-cleanup.md)
- Creating watchers inside async callbacks → See [watch-async-creation-memory-leak](reference/watch-async-creation-memory-leak.md)
- Watcher never triggers for reactive object properties → See [watch-reactive-property-getter](reference/watch-reactive-property-getter.md)
- Async watchEffect misses dependencies after await → See [watcheffect-async-dependency-tracking](reference/watcheffect-async-dependency-tracking.md)
- DOM reads are stale inside watcher callbacks → See [watch-flush-timing](reference/watch-flush-timing.md)
- Deep watchers report identical old/new values → See [watch-deep-same-object-reference](reference/watch-deep-same-object-reference.md)
- watchEffect runs before template refs update → See [watcheffect-flush-post-for-refs](reference/watcheffect-flush-post-for-refs.md)

### Components
- Child component throws "component not found" error → See [local-components-not-in-descendants](reference/local-components-not-in-descendants.md)
- Click listener doesn't fire on custom component → See [click-events-on-components](reference/click-events-on-components.md)
- Parent can't access child ref data in script setup → See [component-ref-requires-defineexpose](reference/component-ref-requires-defineexpose.md)
- HTML template parsing breaks Vue component syntax → See [in-dom-template-parsing-caveats](reference/in-dom-template-parsing-caveats.md)
- Wrong component renders due to naming collisions → See [component-naming-conflicts](reference/component-naming-conflicts.md)
- Parent styles don't apply to multi-root component → See [multi-root-component-class-attrs](reference/multi-root-component-class-attrs.md)

### Props & Emits
- Variables referenced in defineProps cause errors → See [prop-defineprops-scope-limitation](reference/prop-defineprops-scope-limitation.md)
- Component emits undeclared event causing warnings → See [declare-emits-for-documentation](reference/declare-emits-for-documentation.md)
- defineEmits used inside function or conditional → See [defineEmits-must-be-top-level](reference/defineEmits-must-be-top-level.md)
- defineEmits has both type and runtime arguments → See [defineEmits-no-runtime-and-type-mixed](reference/defineEmits-no-runtime-and-type-mixed.md)
- Native event listeners not responding to clicks → See [native-event-collision-with-emits](reference/native-event-collision-with-emits.md)
- Component event fires twice when clicking → See [undeclared-emits-double-firing](reference/undeclared-emits-double-firing.md)

### Templates
- Getting template compilation errors with statements → See [template-expressions-restrictions](reference/template-expressions-restrictions.md)
- "Cannot read property of undefined" runtime errors → See [v-if-null-check-order](reference/v-if-null-check-order.md)
- Dynamic directive arguments not working properly → See [dynamic-argument-constraints](reference/dynamic-argument-constraints.md)
- v-else elements rendering unconditionally always → See [v-else-must-follow-v-if](reference/v-else-must-follow-v-if.md)
- Mixing v-if with v-for causes precedence bugs and migration breakage → See [no-v-if-with-v-for](reference/no-v-if-with-v-for.md)
- Template function calls mutating state cause unpredictable re-render bugs → See [template-functions-no-side-effects](reference/template-functions-no-side-effects.md)
- Child components in loops showing undefined data → See [v-for-component-props](reference/v-for-component-props.md)
- Array order changing after sorting or reversing → See [v-for-computed-reverse-sort](reference/v-for-computed-reverse-sort.md)
- List items disappearing or swapping state unexpectedly → See [v-for-key-attribute](reference/v-for-key-attribute.md)
- Getting off-by-one errors with range iteration → See [v-for-range-starts-at-one](reference/v-for-range-starts-at-one.md)
- v-show or v-else not working on template elements → See [v-show-template-limitation](reference/v-show-template-limitation.md)

### Template Refs
- Ref becomes null when element is conditionally hidden → See [template-ref-null-with-v-if](reference/template-ref-null-with-v-if.md)
- Ref array indices don't match data array in loops → See [template-ref-v-for-order](reference/template-ref-v-for-order.md)
- Refactoring template ref names breaks silently in code → See [use-template-ref-vue35](reference/use-template-ref-vue35.md)

### Forms & v-model
- Initial form values not showing when using v-model → See [v-model-ignores-html-attributes](reference/v-model-ignores-html-attributes.md)
- Textarea content changes not updating the ref → See [textarea-no-interpolation](reference/textarea-no-interpolation.md)
- iOS users cannot select dropdown first option → See [select-initial-value-ios-bug](reference/select-initial-value-ios-bug.md)
- Parent and child components have different values → See [define-model-default-value-sync](reference/define-model-default-value-sync.md)
- Object property changes not syncing to parent → See [definemodel-object-mutation-no-emit](reference/definemodel-object-mutation-no-emit.md)
- Real-time search/validation broken for Chinese/Japanese input → See [v-model-ime-composition](reference/v-model-ime-composition.md)
- Number input returns empty string instead of zero → See [v-model-number-modifier-behavior](reference/v-model-number-modifier-behavior.md)
- Custom checkbox values not submitted in forms → See [checkbox-true-false-value-form-submission](reference/checkbox-true-false-value-form-submission.md)

### Events & Modifiers
- Chaining multiple event modifiers produces unexpected results → See [event-modifier-order-matters](reference/event-modifier-order-matters.md)
- Keyboard shortcuts don't fire with system modifier keys → See [keyup-modifier-timing](reference/keyup-modifier-timing.md)
- Keyboard shortcuts fire with unintended modifier combinations → See [exact-modifier-for-precise-shortcuts](reference/exact-modifier-for-precise-shortcuts.md)
- Combining passive and prevent modifiers break