Question 1

What are Vue directives?

Accepted Answer

Template annotations that apply reactive behavior to DOM (v-if, v-for, v-model, v-show, etc.). Built-ins cover common cases; custom directives handle low-level DOM integrations.

Question 2

v-if vs v-show?

Accepted Answer

v-if conditionally creates/destroys; v-show toggles display CSS. Use v-if for rarely shown costly trees; v-show for frequent toggles.

Question 3

v-for key best practices?

Accepted Answer

Always provide a stable unique key; avoid index when list reorders/filters. Keys preserve component state correctly across patches.

Question 4

v-model modifiers — .lazy .number .trim?

Accepted Answer

Alter when/how the model updates from inputs. Built-in modifiers cover common form needs; components can support custom modifiers.

Question 5

What does v-bind / v-on shorthand look like?

Accepted Answer

:attr for bind, @event for on; can bind objects of attributes/listeners. Object bind is powerful for forwarding. Prefer clarity in complex templates.

Question 6

Custom directives — when preferred over components?

Accepted Answer

When you need direct DOM access that isn't worth a wrapper component (focus, analytics hook). Prefer components/composables for most UI. Directives are escape hatches.

Question 7

Directive hooks in Vue 3 (created/mounted/updated/...)?

Accepted Answer

Lifecycle for the element the directive is bound to. Clean up in beforeUnmount/unmounted. Avoid assuming component instance internals.

Question 8

v-html security concerns?

Accepted Answer

Renders raw HTML—XSS risk if content is user-controlled. Sanitize thoroughly or avoid. Prefer text interpolation.

Question 9

v-memo — what does it do?

Accepted Answer

Memoizes a sub-tree until dependency values change—perf optimization for heavy lists. Use selectively after measuring. Wrong deps serve stale UI.

Question 10

Common v-for + v-if pitfall?

Accepted Answer

Don't use them on the same element; filter computed lists then v-for. Vue 3 treats them differently than Vue 2—still prefer computed filtering.

Directives Vue.js Interview Questions

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