Vue interviews focus on the reactivity system, the Composition API, and component communication. Below are the most common questions with model answers. Junior: core theory, definitions, and simple practical cases.
ref wraps any value and you reach it through .value in script, though templates unwrap it for you. reactive takes an object and returns a reactive proxy with no wrapper. The practical rule is ref for everything, because destructuring a reactive object loses reactivity and that surprises people every time.
computed derives a value and caches it until a dependency changes — it must be pure and return something. watch runs a side effect when something changes: a request, writing to storage. Using watch to set another piece of state is usually a computed that has not been recognised yet.
v-if adds and removes the element from the DOM, so the component is created and destroyed. v-show leaves it there and toggles CSS. v-if when it rarely changes or is expensive to render, v-show when it toggles often — a tab that flips constantly should not be rebuilding its subtree.
So Vue can match items between renders instead of assuming position. Without a stable key it patches by index, which reuses the wrong DOM node — a checked checkbox stays on the row that took that position rather than following its item. The index is a key in name only for anything reorderable.
By emitting an event the parent listens for. Props go down, events go up — a child does not mutate a prop, and Vue warns when it tries. defineModel or the v-model pattern is that same pair with a naming convention on top.
onMounted for anything needing the DOM or a first fetch, onUnmounted to undo it — a listener, a timer, a subscription. onUpdated is rarely the right answer and is often where infinite loops start. In the Composition API these are functions called inside setup rather than options on the component.
In a real interview you speak under pressure. Cam asks these same questions, scores every answer, and shows exactly what to fix.
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