Frontend Interview Questions 2026

Below is a comprehensive list of standard Frontend interview questions in 2026, classified by knowledge groups from foundation to in-depth practical processing situations.

Event Loop & Task Prioritization: Explain the difference in priority between Microtask queue (Promise, async/await) and Macrotask queue (setTimeout, I/O). Why can an infinite microtask loop cause the browser to stop responding completely?
Memory Management: How does the "Mark-and-Sweep" garbage collection mechanism work? How to detect memory leaks in complex SPA applications and what role does WeakMap/WeakSet play in preventing this?
Object Copying Mechanics: Distinguish between shallow copy and deep copy. Compare the performance and limitations of structuredClone(), JSON.parse(JSON.stringify()) and lodash.cloneDeep.
Reference Logic: If the variable a is an object and we assign b = a, how does changing the properties of b affect it? a? What algorithm is commonly used by libraries to copy nested objects?
When should Promise.all be used instead of sequential await commands to optimize network response time? Explain a scenario where Promise.allSettled brings more stability to the system when handling a heterogeneous list of requests.
Conditional Performance: Distinguish between the execution mechanisms of switch and if-else. Why is switch usually faster when there are a large number of conditions and what is the concept of "jump table" in the compiler?
TypeScript Evolution: Why is the 2026 trend favoring the use of "String Literal Unions" combined with as const rather than the traditional Enum? Analysis of the impact on bundle size and type safety.
Advanced Typing: Explains how the infer keyword works in conditional types and the benefits of the satisfies operator compared to coercion with as.
Memoization Logic: Hook Can useMemo remember a function definition?
useCallback Nuances: In addition to optimizing re-render performance, are there other important use cases for useCallback related to referential stability?
Internal Hook Storage: Memoized values values) is actually stored in React's Fiber data structure? Why is the order of calling Hooks considered "sacred"?
useMemo vs useEffect: Let's give an example of using useMemo and useEffect with the same internal logic but with different results in terms of user experience or execution timing.
DOM Synchronization: What is the runtime and intended use difference between useEffect and useLayoutEffect? When will incorrect use of Hooks cause UI flickering?
Function Component Lifecycle: Please describe in detail the lifecycle of a function component using useEffect. When exactly will the clean-up function be executed?
Rules of Hooks:Why can't Hooks be called in loops, conditional statements, or nested functions?
useRef Mechanics: How does useRef work under the Fiber hood? Why does React 19 remove forwardRef and what is the new mechanism to pass ref?
Context API Optimization: Optimization strategies to prevent the entire child component tree from being re-rendered when only a portion of the value in the Context changes?
New React 19 Hooks: Explain how it works and the problem which the hooks useActionState, useOptimistic, and the use() function resolve.
from server? Explain the role of initialization data in this process.
Rendering Comparison: Distinguish in detail the rendering strategies: SSG, SSR, ISR and PPR (Partial Prerendering). How does PPR solve the "Network Waterfall" problem?
How to pass data from a Server Component to a Client Component without violating serialization rules? Why is it not allowed to pass functions or class instances directly across this boundary?
Caching Architecture: How to use new APIs like revalidateTag(), updateTag() and use cache directive (Next.js 16) to explicitly control data freshness.

Tailwind v4 Oxide Engine: When building an application, does Tailwind v4 include the entire CSS library in the build package or only the classes that are actually used? Explain the "Source Detection" mechanism.
Critical Rendering Paths (CRP) Deep Dive: How will the browser handle a