43:[{"uid":"136bm5n0g456","question":"How would you complete this function to implement a retry mechanism with exponential backoff for failed API calls?","createdAt":"$D2025-01-07T21:56:35.701Z","updatedAt":"$D2025-01-31T22:40:38.455Z","questionDate":"","answerResource":null,"correctAnswer":"136bm5n0g452","codeSnippet":"

async function fetchWithRetry(url, options = {}, maxRetries = 3) {\n    let retryCount = 0;\n    let lastError = null;\n\n    const calculateBackoff = (attempt) => {\n        return Math.min(1000 * Math.pow(2, attempt), 10000);\n    };\n\n    while (retryCount <= maxRetries) {\n        try {\n            _______________________________\n            _______________________________\n            _______________________________\n            return response;\n        } catch (error) {\n            lastError = error;\n            if (retryCount === maxRetries) break;\n            \n            const backoffTime = calculateBackoff(retryCount);\n            retryCount++;\n            \n            await new Promise(resolve => setTimeout(resolve, backoffTime));\n        }\n    }\n    \n    throw new Error(`Failed after ${maxRetries} retries: ${lastError.message}`);\n}

","hint":"Think about proper error handling and response validation in the context of HTTP requests.","dailyQuestion":false,"difficulty":"MEDIUM","customQuestion":false,"slug":"implement-retry-mechanism-exponential-backoff-api-calls","slugGenerated":true,"description":null,"title":"Implementing Exponential Backoff Retry Mechanism for Failed API Fetch Requests in JavaScript","questionType":"MULTIPLE_CHOICE","expectedParams":null,"functionName":null,"returnType":null,"testCases":null,"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false},{"uid":"136bm5n0m8rb","question":"Complete the WebSocket manager to implement automatic reconnection with backoff:","createdAt":"$D2025-01-07T22:01:21.619Z","updatedAt":"$D2025-01-31T22:40:38.455Z","questionDate":"","answerResource":null,"correctAnswer":"136bm5n0m8r7","codeSnippet":"

class WSManager {\n    constructor(url) {\n        this.url = url;\n        this.reconnectAttempts = 0;\n        this.maxReconnectAttempts = 5;\n        this.messageQueue = [];\n        this.handlers = new Map();\n    }\n\n    connect() {\n        this.ws = new WebSocket(this.url);\n        \n        this.ws.onopen = () => {\n            ______________________________\n            ______________________________\n        };\n\n        this.ws.onclose = () => {\n            ______________________________\n            ______________________________\n            ______________________________\n        };\n    }\n\n    send(message) {\n        if (this.ws?.readyState === WebSocket.OPEN) {\n            this.ws.send(JSON.stringify(message));\n        } else {\n            this.messageQueue.push(message);\n        }\n    }\n}

","hint":"Consider error recovery, message delivery guarantees, and exponential backoff.","dailyQuestion":false,"difficulty":"HARD","customQuestion":false,"slug":"implement-websocket-auto-reconnection-backoff","slugGenerated":true,"description":null,"title":"Implementing WebSocket Auto-Reconnection with Exponential Backoff in JavaScript","questionType":"MULTIPLE_CHOICE","expectedParams":null,"functionName":null,"returnType":null,"testCases":null,"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false},{"uid":"136bm5n105mv","question":"Complete the missing code in this custom form validation hook:","createdAt":"$D2025-01-07T22:12:10.755Z","updatedAt":"$D2025-01-31T22:40:38.455Z","questionDate":"","answerResource":null,"correctAnswer":"136bm5n105mt","codeSnippet":"

function useFormValidation(initialState) {\n    const [values, setValues] = useState(initialState);\n    const [errors, setErrors] = useState({});\n    const [isSubmitting, setIsSubmitting] = useState(false);\n\n    useEffect(() => {\n        if (isSubmitting) {\n            ________________________\n            ________________________\n            ________________________\n        }\n    }, [values, isSubmitting]);\n\n    function handleChange(event) {\n        const { name, value } = event.target;\n        setValues(prev => ({\n            ...prev,\n            [name]: value\n        }));\n    }\n\n    function handleSubmit(event) {\n        event.preventDefault();\n        setErrors(validate(values));\n        setIsSubmitting(true);\n    }\n\n    return {\n        values,\n        errors,\n        handleChange,\n        handleSubmit,\n        isSubmitting\n    };\n}

","hint":"Consider state updates and validation timing.","dailyQuestion":false,"difficulty":"MEDIUM","customQuestion":false,"slug":"complete-custom-form-validation-hook-react","slugGenerated":true,"description":null,"title":"React Custom Form Validation Hook: Completing the useEffect Logic for Error Handling","questionType":"MULTIPLE_CHOICE","expectedParams":null,"functionName":null,"returnType":null,"testCases":null,"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false},{"uid":"1f3qm5k0kxz2","question":"Your authentication system needs to securely store user tokens. What's wrong with this implementation?","createdAt":"$D2025-01-05T19:37:02.458Z","updatedAt":"$D2025-01-31T22:40:38.455Z","questionDate":"","answerResource":null,"correctAnswer":"1f3qm5k0kxz0","codeSnippet":"

class TokenManager {\n  #tokens = new Map();\n  \n  constructor() {\n    this.checkTokens();\n    setInterval(this.checkTokens.bind(this), 60000);\n  }\n\n  async checkTokens() {\n    for (let [userId, tokenData] of this.#tokens) {\n      if (this.isExpired(tokenData)) {\n        this.#tokens.delete(userId);\n        await this.refreshToken(userId);\n      }\n    }\n  }\n\n  isExpired({ expiresAt }) {\n    return Date.now() >= expiresAt;\n  }\n\n  async refreshToken(userId) {\n    try {\n      const response = await fetch('/api/refresh', {\n        method: 'POST',\n        body: JSON.stringify({ userId })\n      });\n      const data = await response.json();\n      this.#tokens.set(userId, {\n        token: data.token,\n        expiresAt: Date.now() + data.expiresIn\n      });\n    } catch (error) {\n      console.error('Token refresh failed:', error);\n    }\n  }\n}

","hint":"Think about what happens if multiple tokens expire at the same time","dailyQuestion":false,"difficulty":"HARD","customQuestion":false,"slug":"security-issues-token-manager-implementation","slugGenerated":true,"description":null,"title":"Security Issues in Async Token Manager Implementation with Error Handling","questionType":"MULTIPLE_CHOICE","expectedParams":null,"functionName":null,"returnType":null,"testCases":null,"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false},{"uid":"1f3qm5k1mv1l","question":"Fill in the missing code to create a custom React hook that manages form validation with dynamic rules:","createdAt":"$D2025-01-05T20:06:31.589Z","updatedAt":"$D2025-01-31T22:40:38.455Z","questionDate":"","answerResource":null,"correctAnswer":"1f3qm5k1mv1h","codeSnippet":"

function useFormValidation(initialValues, validationSchema) {\n  const [values, setValues] = useState(initialValues);\n  const [errors, setErrors] = useState({});\n  const [isSubmitting, setIsSubmitting] = useState(false);\n\n  // Missing validation logic here\n  \n  const handleChange = (event) => {\n    const { name, value } = event.target;\n    setValues(prev => ({\n      ...prev,\n      [name]: value\n    }));\n  };\n\n  const handleSubmit = async (onSubmit) => {\n    setIsSubmitting(true);\n    const validationErrors = await validateValues(values);\n    setErrors(validationErrors);\n    \n    if (Object.keys(validationErrors).length === 0) {\n      await onSubmit(values);\n    }\n    setIsSubmitting(false);\n  };\n\n  return { values, errors, isSubmitting, handleChange, handleSubmit };\n}

","hint":"Consider how the validation schema might be structured and how to handle both synchronous and asynchronous validation rules.","dailyQuestion":false,"difficulty":"MEDIUM","customQuestion":false,"slug":"create-custom-react-hook-form-validation","slugGenerated":true,"description":null,"title":"Creating a Custom React Hook for Dynamic Form Validation with Error Handling","questionType":"MULTIPLE_CHOICE","expectedParams":null,"functionName":null,"returnType":null,"testCases":null,"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false},{"uid":"1p3dm5ww0hgp","question":"You're building a modern e-commerce platform that needs to fetch product data while handling loading and error states elegantly. The product team wants to implement React Suspense for a better user experience. How would you properly implement data fetching with Suspense while ensuring the code follows React 18's best practices and handles cache invalidation?","createdAt":"$D2025-01-14T19:50:09.764Z","updatedAt":"$D2025-01-31T22:40:38.455Z","questionDate":"","answerResource":null,"correctAnswer":"1p3dm5ww0hgl","codeSnippet":"$58","hint":"Think about how Suspense works with promises and what should happen during different states of the promise lifecycle. Consider how throwing promises is used in React's Suspense pattern.","dailyQuestion":false,"difficulty":"HARD","customQuestion":false,"slug":"implement-react-suspense-data-fetching-ecommerce","slugGenerated":true,"description":null,"title":"Dynamic Data Fetching with Suspense","questionType":"MULTIPLE_CHOICE","expectedParams":null,"functionName":null,"returnType":null,"testCases":null,"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false},{"uid":"2258m5iopuxa","question":"Your team is building a real-time collaborative document editor. You need to implement a debounced auto-save function that prevents too many API calls while users are typing. What's missing in the code below to make it work correctly?","createdAt":"$D2025-01-04T21:17:10.218Z","updatedAt":"$D2025-01-31T22:40:38.455Z","questionDate":"2025-01-26","answerResource":null,"correctAnswer":"2258m5iopux7","codeSnippet":"

class DocumentEditor {\n    constructor() {\n        this.content = '';\n        this.lastSaved = null;\n        this.saveTimeout = null;\n    }\n\n    handleUserInput(newContent) {\n        this.content = newContent;\n        // Missing debounce implementation\n        _______________\n    }\n\n    async saveToServer() {\n        try {\n            await fetch('/api/save', {\n                method: 'POST',\n                body: JSON.stringify({ content: this.content }),\n                headers: { 'Content-Type': 'application/json' }\n            });\n            this.lastSaved = new Date();\n        } catch (error) {\n            console.error('Failed to save:', error);\n        }\n    }\n}

","hint":"Think about the difference between setTimeout and setInterval, and what happens to existing timeouts when new content arrives.","dailyQuestion":true,"difficulty":"HARD","customQuestion":false,"slug":"implement-debounced-autosave-collaborative-editor","slugGenerated":true,"description":null,"title":"Implementing Debounced Auto-Save in a Real-Time Collaborative Document Editor","questionType":"MULTIPLE_CHOICE","expectedParams":null,"functionName":null,"returnType":null,"testCases":null,"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false},{"uid":"2258m5iphsjc","question":"You're building a simple e-commerce product card in React. The card shows a loading state while the product image loads, and handles errors if the image fails to load. What's missing in this implementation?","createdAt":"$D2025-01-04T21:38:53.492Z","updatedAt":"$D2025-01-31T22:40:38.455Z","questionDate":"","answerResource":null,"correctAnswer":"2258m5iphsj9","codeSnippet":"

function ProductCard({ product }) {\n    const [imageStatus, setImageStatus] = useState('loading');\n    \n    // missing code here\n    _______________\n\n    return (\n        <div className=\"card\">\n            <div className=\"image-container\">\n                {imageStatus === 'loading' && <LoadingSpinner />}\n                {imageStatus === 'error' && <ErrorIcon />}\n                <img \n                    src={product.imageUrl}\n                    alt={product.name}\n                    className={imageStatus === 'success' ? 'visible' : 'hidden'}\n                />\n            </div>\n            <h3>{product.name}</h3>\n            <p>${product.price}</p>\n        </div>\n    );\n}

","hint":"Think about when the image loading code should run and what dependencies it needs to track.","dailyQuestion":false,"difficulty":"EASY","customQuestion":false,"slug":"react-product-card-image-loading-error-handling","slugGenerated":true,"description":null,"title":"React: Implementing Image Loading States and Error Handling in Product Card Component","questionType":"MULTIPLE_CHOICE","expectedParams":null,"functionName":null,"returnType":null,"testCases":null,"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false},{"uid":"2258m5ipk2fy","question":"Your team is building a form validation system that needs to check user input against multiple rules. The validation should stop at the first failure and return the error message. What's wrong with this implementation?","createdAt":"$D2025-01-04T21:40:39.642Z","updatedAt":"$D2025-01-31T22:40:38.455Z","questionDate":"2025-01-30","answerResource":null,"correctAnswer":"2258m5ipk2fu","codeSnippet":"

const validators = {\n    required: (value) => !value ? \"This field is required\" : null,\n    minLength: (value, min) => value.length < min ? `Minimum length is ${min}` : null,\n    email: (value) => !value.includes('@') ? \"Invalid email format\" : null,\n    password: (value) => !/[A-Z]/.test(value) ? \"Must contain uppercase letter\" : null\n};\n\nfunction validateField(value, rules) {\n    const errors = Object.entries(rules)\n        .map(([rule, param]) => {\n            if (validators[rule]) {\n                return validators[rule](value, param);\n            }\n            return null;\n        })\n        .filter(Boolean);\n    \n    return errors[0] || null;\n}\n\n// Usage example:\nconst rules = {\n    required: true,\n    minLength: 8,\n    password: true\n};\n\nconst result = validateField(\"password123\", rules);

","hint":"Look at how the errors are collected and returned. Is this the most efficient approach?","dailyQuestion":true,"difficulty":"MEDIUM","customQuestion":false,"slug":"form-validation-early-return-implementation-issue","slugGenerated":true,"description":null,"title":"How to Fix Form Validation That Doesn't Stop at First Error in JavaScript","questionType":"MULTIPLE_CHOICE","expectedParams":null,"functionName":null,"returnType":null,"testCases":null,"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false},{"uid":"2258m5ips47j","question":"You're building a comment system where users can write, edit, and delete their comments. The system needs to prevent duplicate submissions and handle loading states. What's missing in this implementation?","createdAt":"$D2025-01-04T21:46:55.178Z","updatedAt":"$D2025-01-31T22:40:38.455Z","questionDate":"","answerResource":null,"correctAnswer":"2258m5ips47i","codeSnippet":"$59","hint":"Think about data validation and cleanup after submission.","dailyQuestion":false,"difficulty":"MEDIUM","customQuestion":false,"slug":"react-comment-system-duplicate-submission-handling","slugGenerated":true,"description":null,"title":"How to Implement a React Comment System with Form Validation and Loading States","questionType":"MULTIPLE_CHOICE","expectedParams":null,"functionName":null,"returnType":null,"testCases":null,"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false}]