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Bộ lọc
Which of the following is NOT a JavaScript primitive data type?
JavaScript
Data Types
Cơ bản
4 lựa chọn
Which operator is used to check the data type of a variable in JavaScript?
JavaScript
Type Checking
Cơ bản
4 lựa chọn
What does `typeof null` return?
JavaScript
Type Checking
Trung bình
4 lựa chọn
How do null, undefined, and an undeclared variable differ?
JavaScript
Null Undefined
Trung bình
4 lựa chọn
Which statement about var, let, and const is correct?
JavaScript
Variables
Cơ bản
4 lựa chọn
Which is true about reassignment and redeclaration?
JavaScript
Variables
Trung bình
4 lựa chọn
Why is it a good idea to avoid polluting the global scope?
JavaScript
Scope
Trung bình
4 lựa chọn
Which is NOT a common way to convert a string to a number in JavaScript?
JavaScript
Conversion
Cơ bản
4 lựa chọn
How do you embed an expression inside a template literal?
JavaScript
Template Literals
Cơ bản
4 lựa chọn
In a tagged template, what does the tag function receive as its first argument?
JavaScript
Tagged Templates
Nâng cao
4 lựa chọn
What does the spread operator (...) do with an array like [...arr]?
JavaScript
Spread
Cơ bản
4 lựa chọn
What are Symbols primarily used for?
JavaScript
Symbols
Trung bình
4 lựa chọn
Does `Symbol('key') === Symbol('key')` evaluate to true?
JavaScript
Symbols
Nâng cao
4 lựa chọn
What is a JavaScript Proxy used for?
JavaScript
Proxies
Trung bình
4 lựa chọn
What is hoisting in JavaScript?
JavaScript
Hoisting
Cơ bản
4 lựa chọn
Accessing a `let` variable before its declaration results in:
JavaScript
Hoisting
Trung bình
4 lựa chọn
What value do you get by accessing a `var` variable before its initialization?
JavaScript
Hoisting
Trung bình
4 lựa chọn
Which are hoisted such that they can be called before their definition?
JavaScript
Hoisting
Trung bình
4 lựa chọn
How can you best avoid problems caused by hoisting?
JavaScript
Hoisting
Cơ bản
4 lựa chọn
What is the key difference between == and === in JavaScript?
JavaScript
Equality
Cơ bản
4 lựa chọn
What is a common legitimate use of the loose equality operator ==?
JavaScript
Equality
Trung bình
4 lựa chọn
Which loop iterates over an object's enumerable properties, including inherited ones?
JavaScript
Iteration
Trung bình
4 lựa chọn
What is the difference between break and continue?
JavaScript
Control Flow
Cơ bản
4 lựa chọn
What is the syntax of the ternary operator?
JavaScript
Operators
Cơ bản
4 lựa chọn
Which array method gives you both the element and its index in the callback?
JavaScript
Arrays
Cơ bản
4 lựa chọn
What does the switch statement do when no case matches?
JavaScript
Control Flow
Cơ bản
4 lựa chọn
What do rest parameters (...args) do?
JavaScript
Functions
Cơ bản
4 lựa chọn
How do spread and rest syntax differ, despite sharing the ... token?
JavaScript
Spread Rest
Trung bình
4 lựa chọn
What must an iterator object implement?
JavaScript
Iterators Generators
Nâng cao
4 lựa chọn
How is a generator function declared?
JavaScript
Iterators Generators
Nâng cao
4 lựa chọn
What is the difference between `function foo(){}` and `var foo = function(){}`?
JavaScript
Functions
Trung bình
4 lựa chọn
What is the difference between a parameter and an argument?
JavaScript
Functions
Cơ bản
4 lựa chọn
What is a key benefit of arrow functions in callbacks?
JavaScript
Functions
Cơ bản
4 lựa chọn
What does `const p = Person()` do if Person is meant to be a constructor?
JavaScript
Constructors
Trung bình
4 lựa chọn
What defines a higher-order function?
JavaScript
Higher Order Functions
Trung bình
4 lựa chọn
What is a callback function?
JavaScript
Callbacks
Cơ bản
4 lựa chọn
What is a typical use case for anonymous functions?
JavaScript
Anonymous Functions
Cơ bản
4 lựa chọn
What is essential to prevent infinite recursion?
JavaScript
Recursion
Trung bình
4 lựa chọn
When is a default parameter's value used?
JavaScript
Default Parameters
Cơ bản
4 lựa chọn
Why does `function foo(){}();` fail as an IIFE, and how do you fix it?
JavaScript
Iife
Nâng cao
4 lựa chọn
Which is NOT a standard way to create an object in JavaScript?
JavaScript
Objects
Cơ bản
4 lựa chọn
When must you use bracket notation instead of dot notation?
JavaScript
Objects
Trung bình
4 lựa chọn
Which array method transforms each element and returns a new array?
JavaScript
Arrays
Cơ bản
4 lựa chọn
Which method can add or remove elements at any position in an array?
JavaScript
Arrays
Trung bình
4 lựa chọn
Which produces a shallow copy of an object?
JavaScript
Copying
Trung bình
4 lựa chọn
What is the key difference between a shallow copy and a deep copy?
JavaScript
Copying
Nâng cao
4 lựa chọn
Which modern built-in creates a deep copy of an object?
JavaScript
Copying
Trung bình
4 lựa chọn
Which reliably checks for an object's own property (excluding inherited ones)?
JavaScript
Objects
Trung bình
4 lựa chọn
What is the difference between mutable and immutable objects?
JavaScript
Immutability
Trung bình
4 lựa chọn
What does destructuring assignment let you do?
JavaScript
Destructuring
Cơ bản
4 lựa chọn
What does Object.freeze() do?
JavaScript
Object Immutability
Trung bình
4 lựa chọn
How does Object.seal() differ from Object.freeze()?
JavaScript
Object Immutability
Nâng cao
4 lựa chọn
What does Object.preventExtensions() do?
JavaScript
Object Immutability
Nâng cao
4 lựa chọn
What are object getters and setters used for?
JavaScript
Getters Setters
Trung bình
4 lựa chọn
Which property flag controls whether a property can be deleted or its attributes changed?
JavaScript
Property Descriptors
Nâng cao
4 lựa chọn
How can you reliably check whether an object is empty?
JavaScript
Objects
Cơ bản
4 lựa chọn
In the event loop, which queue is fully drained before the next macrotask runs?
JavaScript
Event Loop
Nâng cao
4 lựa chọn
What is the key difference between synchronous and asynchronous functions?
JavaScript
Async
Cơ bản
4 lựa chọn
Why should heavy operations like network requests be asynchronous?
JavaScript
Async
Trung bình
4 lựa chọn
What are the three states of a Promise?
JavaScript
Promises
Cơ bản
4 lựa chọn
Which methods handle a Promise's success and failure?
JavaScript
Promises
Trung bình
4 lựa chọn
What is a benefit of Promises over nested callbacks?
JavaScript
Promises
Trung bình
4 lựa chọn
What does Promise.all() do?
JavaScript
Promises
Trung bình
4 lựa chọn
How does Promise.allSettled() differ from Promise.all()?
JavaScript
Promises
Nâng cao
4 lựa chọn
What does the await keyword do inside an async function?
JavaScript
Async Await
Trung bình
4 lựa chọn
How do you handle errors when using async/await?
JavaScript
Async Await
Trung bình
4 lựa chọn
When are microtasks (like promise callbacks) executed?
JavaScript
Microtasks
Nâng cao
4 lựa chọn
In Node.js, which callback runs before the next event loop iteration begins?
JavaScript
Timers
Nâng cao
4 lựa chọn
How does prototypal inheritance work in JavaScript?
JavaScript
Prototypes
Trung bình
4 lựa chọn
What is at the end of an object's prototype chain?
JavaScript
Prototypes
Trung bình
4 lựa chọn
How does classical inheritance differ from prototypal inheritance?
JavaScript
Inheritance
Trung bình
4 lựa chọn
Which keywords implement inheritance in ES2015 classes?
JavaScript
Classes
Cơ bản
4 lựa chọn
Which is NOT one of the things the `new` keyword does?
JavaScript
New Keyword
Nâng cao
4 lựa chọn
What is the convention when naming a constructor function?
JavaScript
Constructors
Cơ bản
4 lựa chọn
How do ES2015 classes define static methods compared to ES5 constructors?
JavaScript
Classes
Trung bình
4 lựa chọn
Why use an arrow function for a method defined inside a constructor?
JavaScript
Arrow Functions
Nâng cao
4 lựa chọn
How are static class members accessed?
JavaScript
Static Members
Trung bình
4 lựa chọn
What is a closure?
JavaScript
Closures
Trung bình
4 lựa chọn
What does lexical scoping mean?
JavaScript
Scope
Trung bình
4 lựa chọn
Which are the three main types of scope in JavaScript?
JavaScript
Scope
Cơ bản
4 lựa chọn
How can closures create private variables?
JavaScript
Closures
Nâng cao
4 lựa chọn
What is a potential pitfall of closures?
JavaScript
Closures
Trung bình
4 lựa chọn
When a regular function is called as a free function (not a method) in strict mode, what is `this`?
JavaScript
This
Nâng cao
4 lựa chọn
What is `this` inside an arrow function?
JavaScript
This
Trung bình
4 lựa chọn
What does Function.prototype.bind do?
JavaScript
Bind
Trung bình
4 lựa chọn
Which of these is 'explicit binding' of this?
JavaScript
This
Trung bình
4 lựa chọn
A common way to preserve the correct `this` when passing a method as a callback is:
JavaScript
This
Cơ bản
4 lựa chọn
What is the DOM?
JavaScript
Dom
Cơ bản
4 lựa chọn
What is the difference between an HTML attribute and a DOM property?
JavaScript
Dom
Trung bình
4 lựa chọn
How does document.querySelector() differ from document.getElementById()?
JavaScript
Dom
Trung bình
4 lựa chọn
Which method creates a new element to insert into the DOM?
JavaScript
Dom
Cơ bản
4 lựa chọn
How do you attach an event listener to an element?
JavaScript
Events
Cơ bản
4 lựa chọn
What are the three phases of DOM event propagation, in order?
JavaScript
Events
Trung bình
4 lựa chọn
In event bubbling, an event propagates:
JavaScript
Events
Cơ bản
4 lựa chọn
How is event capturing different from event bubbling?
JavaScript
Events
Trung bình
4 lựa chọn
What is event delegation?
JavaScript
Events
Trung bình
4 lựa chọn
How do you stop an event's default action, e.g. a form submitting?
JavaScript
Events
Cơ bản
4 lựa chọn
What is the difference between preventDefault() and stopPropagation()?
JavaScript
Events
Trung bình
4 lựa chọn
What is the key difference between mouseenter and mouseover?
JavaScript
Events
Nâng cao
4 lựa chọn
What is the difference between innerHTML and textContent?
JavaScript
Dom
Trung bình
4 lựa chọn
How do you toggle a CSS class on an element in JavaScript?
JavaScript
Dom
Cơ bản
4 lựa chọn
How does <script defer> behave?
JavaScript
Script Loading
Trung bình
4 lựa chọn
What is the difference between the Window and Document objects?
JavaScript
Bom
Cơ bản
4 lựa chọn
Which client storage mechanism is automatically sent to the server on every HTTP request?
JavaScript
Storage
Trung bình
4 lựa chọn
How does sessionStorage differ from localStorage?
JavaScript
Storage
Trung bình
4 lựa chọn
What does the Fetch API's fetch() function return?
JavaScript
Fetch
Cơ bản
4 lựa chọn
Which is a popular third-party library for making API calls?
JavaScript
Api Calls
Cơ bản
4 lựa chọn
What does AJAX enable?
JavaScript
Ajax
Trung bình
4 lựa chọn
Which is a disadvantage of AJAX?
JavaScript
Ajax
Trung bình
4 lựa chọn
Which is a difference between fetch() and XMLHttpRequest?
JavaScript
Fetch
Nâng cao
4 lựa chọn
How do you cancel an in-flight fetch request?
JavaScript
Abort
Trung bình
4 lựa chọn
How does JSONP bypass the same-origin policy?
JavaScript
Jsonp
Nâng cao
4 lựa chọn
What is a key limitation of Web Workers?
JavaScript
Workers
Trung bình
4 lựa chọn
Which type of worker acts as a network proxy enabling offline caching and push notifications?
JavaScript
Workers
Nâng cao
4 lựa chọn
What does the WebSocket API provide?
JavaScript
Websocket
Trung bình
4 lựa chọn
What is a polyfill?
JavaScript
Polyfills
Trung bình
4 lựa chọn
Which HTML tag shows content when JavaScript is disabled?
JavaScript
Html Js
Cơ bản
4 lựa chọn
What is the Intl namespace object used for?
JavaScript
Intl
Trung bình
4 lựa chọn
Which method checks whether a form input satisfies its validation constraints?
JavaScript
Forms
Trung bình
4 lựa chọn
Which window.history method adds a new entry to the session history without reloading?
JavaScript
History
Trung bình
4 lựa chọn
How can a page and its iframe communicate across origins?
JavaScript
Iframes
Trung bình
4 lựa chọn
How does the DOMContentLoaded event differ from the load event?
JavaScript
Events
Trung bình
4 lựa chọn
How do you redirect the browser to a new URL in JavaScript?
JavaScript
Navigation
Cơ bản
4 lựa chọn
Which API reads query string parameters from the current URL?
JavaScript
Url
Trung bình
4 lựa chọn
How do Server-Sent Events (EventSource) differ from WebSockets?
JavaScript
Server Sent Events
Nâng cao
4 lựa chọn
Which technologies enable Progressive Web Applications (PWAs)?
JavaScript
Pwa
Trung bình
4 lựa chọn
Why are JavaScript modules useful?
JavaScript
Modules
Cơ bản
4 lựa chọn
Which is a difference between CommonJS and ES modules?
JavaScript
Modules
Nâng cao
4 lựa chọn
How do you export a single default value from an ES module?
JavaScript
Modules
Cơ bản
4 lựa chọn
What is a key benefit of a module bundler like Webpack or Vite?
JavaScript
Bundlers
Trung bình
4 lựa chọn
What is tree shaking?
JavaScript
Bundlers
Nâng cao
4 lựa chọn
Where are a JavaScript module's metadata fields (name, version, dependencies) typically defined?
JavaScript
Modules
Cơ bản
4 lựa chọn
Which module system is the official ECMAScript standard, natively supported in browsers and Node?
JavaScript
Modules
Trung bình
4 lựa chọn
Which are the three main categories of JavaScript errors?
JavaScript
Errors
Cơ bản
4 lựa chọn
What is the role of a try...catch block?
JavaScript
Errors
Cơ bản
4 lựa chọn
When does the finally block run?
JavaScript
Errors
Trung bình
4 lựa chọn
How do you create a custom error type in JavaScript?
JavaScript
Errors
Trung bình
4 lựa chọn
What is error propagation?
JavaScript
Errors
Trung bình
4 lựa chọn
What is currying?
JavaScript
Currying
Nâng cao
4 lựa chọn
What does partial application do?
JavaScript
Partial Application
Nâng cao
4 lựa chọn
How do currying and partial application differ?
JavaScript
Currying
Trung bình
4 lựa chọn
What is the difference between a Set and a Map?
JavaScript
Collections
Cơ bản
4 lựa chọn
What is a key characteristic of WeakMap keys compared to Map keys?
JavaScript
Collections
Nâng cao
4 lựa chọn
How do you convert a Set to an array?
JavaScript
Collections
Cơ bản
4 lựa chọn
Which is an advantage of a Map over a plain object?
JavaScript
Collections
Trung bình
4 lựa chọn
How do Sets and Maps compare objects for equality?
JavaScript
Collections
Nâng cao
4 lựa chọn
Which is a common JavaScript performance bottleneck?
JavaScript
Performance
Trung bình
4 lựa chọn
What is the difference between debouncing and throttling?
JavaScript
Performance
Nâng cao
4 lựa chọn
Which technique optimizes DOM manipulation?
JavaScript
Performance
Trung bình
4 lựa chọn
Which helps reduce reflows and repaints?
JavaScript
Performance
Trung bình
4 lựa chọn
What is lazy loading?
JavaScript
Performance
Cơ bản
4 lựa chọn
How do Web Workers improve performance?
JavaScript
Performance
Trung bình
4 lựa chọn
What is caching used for in front-end performance?
JavaScript
Performance
Cơ bản
4 lựa chọn
Which tool provides a Performance panel and audits for analyzing JS performance?
JavaScript
Performance
Cơ bản
4 lựa chọn
Which optimizes network requests?
JavaScript
Performance
Trung bình
4 lựa chọn
Which testing type checks individual components in isolation?
JavaScript
Testing
Cơ bản
4 lựa chọn
What does end-to-end (E2E) testing verify?
JavaScript
Testing
Trung bình
4 lựa chọn
Which is a popular JavaScript testing framework known for integration with React?
JavaScript
Testing
Cơ bản
4 lựa chọn
In Jest, which assertion checks that sum(1,2) equals 3?
JavaScript
Testing
Trung bình
4 lựa chọn
What is the core cycle of Test-Driven Development (TDD)?
JavaScript
Testing
Trung bình
4 lựa chọn
What is the difference between a stub and a mock?
JavaScript
Testing
Nâng cao
4 lựa chọn
How do you test asynchronous code in Jest?
JavaScript
Testing
Trung bình
4 lựa chọn
What does code coverage measure?
JavaScript
Testing
Trung bình
4 lựa chọn
What are design patterns?
JavaScript
Design Patterns
Cơ bản
4 lựa chọn
What does the Singleton pattern guarantee?
JavaScript
Design Patterns
Trung bình
4 lựa chọn
What is the purpose of the Factory pattern?
JavaScript
Design Patterns
Trung bình
4 lựa chọn
How does the Observer pattern work?
JavaScript
Design Patterns
Trung bình
4 lựa chọn
How does the Module pattern achieve encapsulation?
JavaScript
Design Patterns
Nâng cao
4 lựa chọn
What does the Prototype pattern do?
JavaScript
Design Patterns
Trung bình
4 lựa chọn
What does the Decorator pattern allow?
JavaScript
Design Patterns
Nâng cao
4 lựa chọn
What is the Strategy pattern used for?
JavaScript
Design Patterns
Nâng cao
4 lựa chọn
What does the Command pattern encapsulate?
JavaScript
Design Patterns
Nâng cao
4 lựa chọn
Why is extending built-in objects (e.g. Array.prototype) generally discouraged?
JavaScript
Best Practices
Trung bình
4 lựa chọn
What is Cross-Site Scripting (XSS)?
JavaScript
Security
Trung bình
4 lựa chọn
Which mitigates Cross-Site Request Forgery (CSRF)?
JavaScript
Security
Nâng cao
4 lựa chọn
How do you prevent SQL injection?
JavaScript
Security
Trung bình
4 lựa chọn
Which is a best practice for handling sensitive data in JavaScript?
JavaScript
Security
Trung bình
4 lựa chọn
What does a Content Security Policy (CSP) do?
JavaScript
Security
Nâng cao
4 lựa chọn
What does the X-Content-Type-Options security header do?
JavaScript
Security
Trung bình
4 lựa chọn
Which header helps prevent clickjacking?
JavaScript
Security
Trung bình
4 lựa chọn
Why is input validation important for security?
JavaScript
Security
Cơ bản
4 lựa chọn
Which tool checks installed dependencies for known security vulnerabilities?
JavaScript
Security
Trung bình
4 lựa chọn
Which is a common approach for secure authentication in JS applications?
JavaScript
Auth
Trung bình
4 lựa chọn
What does the same-origin policy restrict?
JavaScript
Security
Nâng cao
4 lựa chọn
What is a benefit of enabling 'use strict'?
JavaScript
Strict Mode
Trung bình
4 lựa chọn
Which statement pauses execution to invoke the debugger where supported?
JavaScript
Debugging
Cơ bản
4 lựa chọn
Which algorithm underlies most JavaScript garbage collection?
JavaScript
Garbage Collection
Nâng cao
4 lựa chọn
What does the marking phase of mark-and-sweep do?
JavaScript
Garbage Collection
Trung bình
4 lựa chọn
How are Single Page Applications typically made SEO-friendly?
JavaScript
Spa
Trung bình
4 lựa chọn
What is the standard way to share code between JavaScript files?
JavaScript
Modules
Cơ bản
4 lựa chọn
Which is an advantage of using TypeScript over plain JavaScript?
JavaScript
Typescript
Trung bình
4 lựa chọn
Why is document.write() discouraged in modern web development?
JavaScript
Dom
Trung bình
4 lựa chọn
What kind of technology is React?
React
React Basics
Cơ bản
4 lựa chọn
Which of the following is a core benefit of React's declarative model?
React
React Basics
Trung bình
4 lựa chọn
Why is React's component-based architecture considered a benefit?
React
React Basics
Nâng cao
4 lựa chọn
Which statement best describes a React Element?
React
React Elements
Cơ bản
4 lựa chọn
What is a React Component?
React
React Elements
Trung bình
4 lựa chọn
Which of these is NOT a valid React Node?
React
React Elements
Nâng cao
4 lựa chọn
What does JSX stand for?
React
Jsx
Cơ bản
4 lựa chọn
Into what is the JSX `<div>Hello</div>` typically transformed?
React
Jsx
Trung bình
4 lựa chọn
Which statement about JSX is correct?
React
Jsx
Nâng cao
4 lựa chọn
What is the key difference between state and props?
React
State Props
Cơ bản
4 lựa chọn
How does a child component cause a change to data owned by its parent?
React
State Props
Trung bình
4 lựa chọn
Where should shared state ideally live in React's one-way data flow?
React
State Props
Nâng cao
4 lựa chọn
What is the purpose of the `key` prop when rendering lists?
React
Keys
Cơ bản
4 lựa chọn
A `key` must be unique among which scope?
React
Keys
Trung bình
4 lựa chọn
Changing a component's `key` to a new value causes React to:
React
Keys
Nâng cao
4 lựa chọn
Using array indices as keys is problematic mainly when the list is:
React
Keys
Cơ bản
4 lựa chọn
What is a symptom of incorrectly using array indices as keys?
React
Keys
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4 lựa chọn
When is using an array index as a key actually acceptable?
React
Keys
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In a controlled component, the source of truth for a form input's value is:
React
Controlled Components
Cơ bản
4 lựa chọn
How do you typically read the value of an uncontrolled input?
React
Controlled Components
Trung bình
4 lựa chọn
Which input type is always uncontrolled in React?
React
Controlled Components
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4 lựa chọn
Which is a common pitfall when using React Context?
React
Context
Cơ bản
4 lựa chọn
Will wrapping a consumer in `React.memo` stop it re-rendering when context changes?
React
Context
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4 lựa chọn
For frequently-changing, independent slices of shared state, a good alternative to one big context is:
React
Context
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4 lựa chọn
What do hooks let you do?
React
Hooks
Cơ bản
4 lựa chọn
Which class-era problem did hooks help solve?
React
Hooks
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4 lựa chọn
What makes stateful logic genuinely reusable between function components?
React
Hooks
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4 lựa chọn
Where must React hooks be called?
React
Hooks Rules
Cơ bản
4 lựa chọn
From where are you allowed to call hooks?
React
Hooks Rules
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4 lựa chọn
Which tool helps enforce the rules of hooks?
React
Hooks Rules
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4 lựa chọn
When does `useEffect` run relative to the browser paint?
React
Effects
Cơ bản
4 lựa chọn
When should you prefer `useLayoutEffect` over `useEffect`?
React
Effects
Trung bình
4 lựa chọn
What is true about `useLayoutEffect` during server-side rendering?
React
Effects
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4 lựa chọn
What does the updater (callback) form `setCount(c => c + 1)` guarantee?
React
Setstate
Cơ bản
4 lựa chọn
Calling `setCount(c => c + 1)` twice in the same handler (starting at 0) results in:
React
Setstate
Trung bình
4 lựa chọn
When is the updater form especially important?
React
Setstate
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4 lựa chọn
What does an empty dependency array `[]` in useEffect mean?
React
Effects
Cơ bản
4 lựa chọn
If you omit the dependency array of useEffect entirely, the effect:
React
Effects
Trung bình
4 lựa chọn
What does the dependency array control?
React
Effects
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4 lựa chọn
What is `useRef` primarily used for?
React
Useref
Cơ bản
4 lựa chọn
A common DOM use of useRef is to:
React
Useref
Trung bình
4 lựa chọn
Updating `ref.current` differs from updating state because it:
React
Useref
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4 lựa chọn
What does `useCallback` return?
React
Usecallback
Cơ bản
4 lựa chọn
What is the real benefit of the referential stability useCallback provides?
React
Usecallback
Trung bình
4 lựa chọn
How does the React Compiler (stable in React 19) affect useCallback usage?
React
Usecallback
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4 lựa chọn
What is `useMemo` used for?
React
Usememo
Cơ bản
4 lựa chọn
When is useMemo most appropriate?
React
Usememo
Trung bình
4 lựa chọn
What is the key difference between useMemo and useCallback?
React
Usememo
Nâng cao
4 lựa chọn
What does `useReducer` return?
React
Usereducer
Cơ bản
4 lựa chọn
When is useReducer preferable to useState?
React
Usereducer
Trung bình
4 lựa chọn
What two arguments does useReducer take?
React
Usereducer
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4 lựa chọn
What does the `useId` hook generate?
React
Useid
Cơ bản
4 lựa chọn
Why does useId exist?
React
Useid
Trung bình
4 lựa chọn
Which is an appropriate use of useId?
React
Useid
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4 lựa chọn
What triggers a re-render in React?
React
Rendering
Cơ bản
4 lựa chọn
During a re-render, how does React decide what DOM to update?
React
Rendering
Trung bình
4 lựa chọn
What are React Fragments used for?
React
Fragments
Cơ bản
4 lựa chọn
Which is the shorthand syntax for a React Fragment?
React
Fragments
Trung bình
4 lựa chọn
What was `forwardRef()` historically used for?
React
Refs
Cơ bản
4 lựa chọn
What changed about forwardRef in React 19?
React
Refs
Trung bình
4 lựa chọn
In React 19+, how does a function component receive a forwarded ref?
React
Refs
Nâng cao
4 lựa chọn
What is the most idiomatic way to fully reset a component's state?
React
State Reset
Cơ bản
4 lựa chọn
For a finer-grained reset without remounting, you can:
React
State Reset
Trung bình
4 lựa chọn
Why does changing the key reset state?
React
State Reset
Nâng cao
4 lựa chọn
Why does React recommend against mutating state directly?
React
Immutability
Cơ bản
4 lựa chọn
Mutating state in place can break which of the following?
React
Immutability
Trung bình
4 lựa chọn
What is the correct way to update array state immutably?
React
Immutability
Nâng cao
4 lựa chọn
What do error boundaries do?
React
Error Boundaries
Cơ bản
4 lựa chọn
Which do error boundaries NOT catch?
React
Error Boundaries
Trung bình
4 lựa chọn
How are error boundaries implemented today?
React
Error Boundaries
Nâng cao
4 lựa chọn
Which library encourages testing React components the way users interact with them?
React
Testing
Cơ bản
4 lựa chọn
Which tool is preferred for simulating user interactions in tests?
React
Testing
Trung bình
4 lựa chọn
Which tool is commonly used to mock network calls in React tests?
React
Testing
Nâng cao
4 lựa chọn
What is React hydration?
React
Hydration
Cơ bản
4 lựa chọn
Hydration happens after which step?
React
Hydration
Trung bình
4 lựa chọn
What do React Portals let you do?
React
Portals
Cơ bản
4 lựa chọn
Even though a portal's DOM lives elsewhere, events from it:
React
Portals
Trung bình
4 lựa chọn
Which function creates a portal?
React
Portals
Nâng cao
4 lựa chọn
Which browser extension helps inspect the React component tree?
React
Debugging
Cơ bản
4 lựa chọn
Enabling Strict Mode during development helps by:
React
Debugging
Trung bình
4 lựa chọn
What does React Strict Mode render to the page?
React
Strict Mode
Cơ bản
4 lựa chọn
Which is a benefit of Strict Mode?
React
Strict Mode
Trung bình
4 lựa chọn
What behavior does Strict Mode add to effects in development?
React
Strict Mode
Nâng cao
4 lựa chọn
Which libraries are commonly used to localize React applications?
React
I18n
Cơ bản
4 lựa chọn
With react-i18next, how do you typically render translated text?
React
I18n
Trung bình
4 lựa chọn
What is code splitting in a React application?
React
Code Splitting
Cơ bản
4 lựa chọn
Which React APIs enable code splitting for components?
React
Code Splitting
Trung bình
4 lựa chọn
What does the `fallback` prop of Suspense provide during lazy loading?
React
Code Splitting
Nâng cao
4 lựa chọn
In 2026, what should you adopt first to reduce context-driven re-renders?
React
Context Perf
Cơ bản
4 lựa chọn
Which pattern reduces re-renders for consumers that only dispatch?
React
Context Perf
Trung bình
4 lựa chọn
Which library helps subscribe to a slice of a large context value?
React
Context Perf
Nâng cao
4 lựa chọn
What is a higher order component (HOC)?
React
Hoc
Cơ bản
4 lựa chọn
What is the modern recommendation regarding HOCs?
React
Hoc
Trung bình
4 lựa chọn
Which well-known API is an example of an HOC?
React
Hoc
Nâng cao
4 lựa chọn
What data flow does the Flux pattern enforce?
React
Flux
Cơ bản
4 lựa chọn
In Flux, what is the role of the Dispatcher?
React
Flux
Trung bình
4 lựa chọn
Which modern tools were inspired by Flux?
React
Flux
Nâng cao
4 lựa chọn
In React's one-way data flow, data moves:
React
Data Flow
Cơ bản
4 lựa chọn
React's one-way data flow contrasts with which mechanism?
React
Data Flow
Trung bình
4 lựa chọn
What does the React documentation recommend instead of hand-rolling useEffect + fetch?
React
Async Data
Cơ bản
4 lựa chọn
In React 19, which hook lets a component read a promise directly and suspend?
React
Async Data
Trung bình
4 lựa chọn
A hand-written useEffect + fetch needs which safeguards to avoid bugs?
React
Async Data
Nâng cao
4 lựa chọn
What is server-side rendering (SSR) in React?
React
Ssr
Cơ bản
4 lựa chọn
Which is a benefit of SSR?
React
Ssr
Trung bình
4 lựa chọn
Which API enables streaming SSR in Node?
React
Ssr
Nâng cao
4 lựa chọn
When does static generation (SSG) render pages?
React
Ssg
Cơ bản
4 lựa chọn
What does Incremental Static Regeneration (ISR) add to SSG?
React
Ssg
Trung bình
4 lựa chọn
SSG is best suited for content that:
React
Ssg
Nâng cao
4 lựa chọn
In the presentational vs container pattern, presentational components:
React
Patterns
Cơ bản
4 lựa chọn
What is the modern view on the presentational/container split?
React
Patterns
Trung bình
4 lựa chọn
Which is a common data-fetching pitfall in React?
React
Data Fetching Pitfalls
Cơ bản
4 lựa chọn
Why can fetching data during render cause problems?
React
Data Fetching Pitfalls
Trung bình
4 lựa chọn
What should you account for regarding StrictMode and effects during development?
React
Data Fetching Pitfalls
Nâng cao
4 lựa chọn
What is a render prop?
React
Render Props
Cơ bản
4 lựa chọn
Which is the more common modern form of a render prop?
React
Render Props
Trung bình
4 lựa chọn
What largely replaced render props for sharing stateful logic?
React
Render Props
Nâng cao
4 lựa chọn
Which is a React anti-pattern?
React
Anti Patterns
Cơ bản
4 lựa chọn
Which of these is an anti-pattern related to derived data?
React
Anti Patterns
Trung bình
4 lựa chọn
Why is mirroring props into useState an anti-pattern?
React
Anti Patterns
Nâng cao
4 lựa chọn
Which tool fits purely local component state?
React
State Decision
Cơ bản
4 lựa chọn
React Context is best used for values that:
React
State Decision
Trung bình
4 lựa chọn
How should server state (caching, refetching, invalidation) be handled?
React
State Decision
Nâng cao
4 lựa chọn
What is the composition pattern in React?
React
Composition
Cơ bản
4 lựa chọn
Which is a form of composition in React?
React
Composition
Trung bình
4 lựa chọn
A parent that exposes related sub-components like <Tabs.List> and <Tabs.Panel> is an example of:
React
Composition
Nâng cao
4 lựa chọn
What is the 'virtual DOM' in React?
React
Virtual Dom
Cơ bản
4 lựa chọn
What is the main benefit of the virtual DOM?
React
Virtual Dom
Trung bình
4 lựa chọn
Which terms does the React team now prefer over 'virtual DOM'?
React
Virtual Dom
Nâng cao
4 lựa chọn
What is React Fiber?
React
Fiber
Cơ bản
4 lựa chọn
What key capability does Fiber add to rendering?
React
Fiber
Trung bình
4 lựa chọn
Which features did Fiber make possible that the old stack reconciler could not?
React
Fiber
Nâng cao
4 lựa chọn
What is reconciliation in React?
React
Reconciliation
Cơ bản
4 lựa chọn
What is the comparison step in reconciliation called?
React
Reconciliation
Trung bình
4 lựa chọn
What does React Suspense let you do?
React
Suspense
Cơ bản
4 lựa chọn
Suspense is commonly used together with which API for code splitting?
React
Suspense
Trung bình
4 lựa chọn
What happens immediately when a useState setter is called?
React
Setstate
Cơ bản
4 lựa chọn
How does React handle multiple setState calls in the same event?
React
Setstate
Trung bình
4 lựa chọn
Because state updates are batched and asynchronous, reading the state variable right after calling its setter gives you:
React
Setstate
Nâng cao
4 lựa chọn
