/vue-debug-guides

name: vue-debug-guides
description: 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-st