Frontend
450 bites tagged Frontend — interview questions with model answers, and 60-second explainers.
SvelteKit 2.61 breaks remote functions, adds live queries
SvelteKit 2.61 removes .run() from remote queries and rewrites enhance callbacks, forcing refactors. New query.live() adds async-iterable real-time streams. If you use remote functions, check three breaking changes before upgrading.
Angular v22 stabilizes Signal Forms, Aria, Asynchronous Reactivity APIs
Angular v22 promotes Signal Forms, Angular Aria, and Asynchronous Reactivity APIs from developer preview to production-ready status, giving teams stable primitives for reactive forms, accessibility, and async signals without experimental guardrails.
Angular 21.1 ships with Signal Forms debounce patterns
Angular 21.1 ships with minor fixes. Signal Forms tutorials now show debounced async validators to cut wasted backend API calls. Migration guides for the modern Control Flow syntax are available for apps still on legacy structural directives.
Vue 3.4 Cuts Build Times 44%, Stabilizes defineModel
Vue 3.4 cuts SFC compile times 44% and doubles parser speed while stabilizing defineModel for v-model. The refactored reactivity engine skips redundant computed triggers, reducing re-renders. Upgrade requires Volar 1.8.27+ and matching toolchain versions.
VitePress 1.0 replaces VuePress for docs
VitePress 1.0 replaces VuePress, powering docs for Vite, Pinia, and Vitest. It serves static HTML for SEO, then hydrates into a Vue 3 SPA with sub-100ms edits. Migrate legacy VuePress docs or choose it for new content sites.
Vue 3.5 cuts reactivity memory 56%, adds lazy hydration
Vue 3.5 drops reactivity memory 56% and large arrays up to 10x faster with no breaks. Stable reactive props destructure kills withDefaults boilerplate, while lazy hydration and useId() fix SSR pain points.
How do you debug and fix flaky Cypress E2E tests?
This tests systematic debugging of async UI behavior. A strong answer isolates root causes via logs and screenshots, fixes races with explicit waits or intercepts, and stubs APIs not network timing.
How does ngc work in Angular AOT and what artifacts improve performance?
This tests understanding of AOT build-phase compilation and output. Cover efficient JS output, inlined templates and styles cutting AJAX requests, and removal of compiler payload roughly half of Angular. Red flag: conflating AOT and JIT or calling it bundling.
How would you unit-test a Svelte date utility with Vitest?
This question tests isolating pure logic from Svelte and configuring Vitest. A good answer covers installing Vitest, co-locating a spec file, and asserting known inputs. A red flag is insisting you must mount a Svelte component to test a plain function.
Create a custom synchronous validator for an Angular Reactive Form
Tests your grasp of the ValidatorFn contract and reactive form wiring. A strong answer: a function accepting AbstractControl returns null when valid or an error object when invalid, passed as the second FormControl argument. Red flag: returning booleans.
Explain patch flags and static hoisting in Vue 3's compiler
Tests your grasp of compiler-informed virtual DOM optimizations. A strong answer covers patch flags as bitmap hints for dynamic bindings and static hoisting as extracting static nodes to skip diffing. Red flag: claiming Vue 3 removes the virtual DOM.
How does Svelte compile count += 1 into DOM updates?
Tests if you know Svelte reactivity is compile-time via runes, not runtime proxies. Good answer: $state marks reactive vars; runes are compiler hooks; compiler emits DOM-sync code. Red flag: describing useState or VDOM.
What is the Virtual DOM's role during a Vue state update?
Tests your grasp of Vue's reactive render pipeline. A strong answer: state change triggers a new virtual DOM tree; runtime diffs it against the old tree to apply only necessary real DOM updates. Red flag: saying virtual DOM updates browser DOM directly.
Describe the role of a spy in testing with a framework example
This tests whether you know a spy records calls without replacing original implementation. A strong answer defines the tracking role, picks a concrete Vue or Angular handler, and asserts with toHaveBeenCalled.
How do you test emitted events using Vue Test Utils?
Tests Vue Test Utils event inspection. Strong answer: mount, trigger('click'), then check wrapper.emitted('increment') for the payload array. Remember it returns an array of arrays, one per emission.
What is Angular's TestBed and when would you use it?
Say createComponent returns a fixture with no immediate binding, so await fixture.whenStable before asserting DOM. Your knowledge of TestBed as the component factory and change-detection controller.
Implement virtual scrolling for a large list in Vue
Tests DOM cost awareness and viewport culling. Strong answer: mount only visible nodes plus overscan, recycle DOM on scroll, and preserve total scroll height with a spacer. Red flag: suggesting pagination or naive v-for without keys.
Vue computed vs method: performance difference and when to choose each?
This tests Vue reactivity caching. Answer: computed caches and reruns only when reactive deps change, while methods run each render. Choose computed for derived data; methods for events/args. Red flag: saying computed is always faster or passing arguments.
Vue 3 Composables vs Vue 2 Mixins: differences and problems solved
Tests why Vue replaced mixins with composables for stateful logic reuse. Answers cite property collisions, unclear origin, inflexible config, and weak type inference.
What is a Svelte Action? Write a simple logging action.
Define a function receiving the node, log a message, and optionally return destroy. Whether you understand a Svelte action as a lifecycle function attached to a DOM node via use: and can write its minimal signature.
How to create a singleton Angular auth service
Tests Angular dependency injection and singleton scope. Strong answer: use the Injectable decorator with providedIn set to root for an application-wide singleton, then inject it into components.
How do you implement a data-fetching Composable in Vue 3?
Write useFetch accepting a URL, exposing data, loading, and error refs, then return them. grasp of stateful logic reuse via Vue's Composition API. returning plain vars or using shared singletons instead of factories.
How do you manage router scroll behavior and history position restoration?
Use scrollBehavior to return savedPosition on popstate and top: 0 on new navigations; handle hash anchors and async delays. Your grasp of popstate and centralized router scroll orchestration.
How do you create a dynamic route and access the id parameter?
This tests Vue Router dynamic segment syntax and param access. Define the path with a colon like /products/:id, then read via useRoute().params.id or $route.params.id. A red flag is expecting a remount on param changes or parsing window.location manually.
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