4b:[{"uid":"136bm5n03clt","question":"Complete the missing code to transform an array of user records into a structured report:","createdAt":"$D2025-01-07T21:46:40.141Z","updatedAt":"$D2025-01-31T22:40:38.455Z","questionDate":"","answerResource":null,"correctAnswer":"136bm5n03clp","codeSnippet":"

const users = [\n    { id: 1, name: 'Alice', purchases: [100, 200, 300], status: 'active' },\n    { id: 2, name: 'Bob', purchases: [150, 50], status: 'inactive' },\n    { id: 3, name: 'Charlie', purchases: [400, 600, 100], status: 'active' }\n];\n\nfunction generateUserReport(users) {\n    return users\n        ._____________________\n        ._____________________\n        ._____________________\n}\n\nconst result = generateUserReport(users);\n// Should output: { activeUsers: 2, totalSpent: 1900, averageSpent: 316.67 }

","hint":"Think about the order of operations needed: filtering active users first, then calculating purchase totals, and finally aggregating the results.","dailyQuestion":false,"difficulty":"MEDIUM","customQuestion":false,"slug":"transform-user-records-array-into-structured-report","slugGenerated":true,"description":null,"title":"How to Transform User Data Array into Summary Report using JavaScript Array Methods","questionType":"MULTIPLE_CHOICE","expectedParams":null,"functionName":null,"returnType":null,"testCases":null,"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false},{"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":"136bm5n0ibhg","question":"What's the correct implementation to create a reactive object that logs all property access and modifications?","createdAt":"$D2025-01-07T21:58:18.528Z","updatedAt":"$D2025-01-31T22:40:38.455Z","questionDate":"","answerResource":null,"correctAnswer":"136bm5n0ibhd","codeSnippet":"

function createReactiveObject(target) {\n    const handlers = {\n        get(target, property, receiver) {\n            _______________________________\n        },\n        set(target, property, value, receiver) {\n            _______________________________\n            _______________________________\n        }\n    };\n\n    return new Proxy(target, handlers);\n}\n\nconst user = createReactiveObject({\n    name: 'John',\n    age: 30\n});\n\nuser.name = 'Jane';  // Should log modification\nconsole.log(user.age);  // Should log access

","hint":"Consider how to properly handle property access and modification while avoiding infinite loops.","dailyQuestion":false,"difficulty":"HARD","customQuestion":false,"slug":"create-reactive-object-proxy-logging-properties","slugGenerated":true,"description":null,"title":"How to Create a JavaScript Proxy Object with Property Access Tracking and Logging","questionType":"MULTIPLE_CHOICE","expectedParams":null,"functionName":null,"returnType":null,"testCases":null,"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false},{"uid":"136bm5n0kc6c","question":"What's missing in this custom iterator implementation that uses generators to process a large dataset in chunks?","createdAt":"$D2025-01-07T21:59:52.736Z","updatedAt":"$D2025-01-31T22:40:38.455Z","questionDate":"","answerResource":null,"correctAnswer":"136bm5n0kc69","codeSnippet":"

class DatasetProcessor {\n    constructor(dataset, chunkSize = 1000) {\n        this.dataset = dataset;\n        this.chunkSize = chunkSize;\n    }\n\n    *chunkGenerator() {\n        ______________________________\n        ______________________________\n        ______________________________\n    }\n\n    async processChunks(processor) {\n        for (const chunk of this.chunkGenerator()) {\n            await processor(chunk);\n            console.log(`Processed chunk of ${chunk.length} items`);\n        }\n    }\n}\n\nconst processor = new DatasetProcessor([/* large dataset */]);\nprocessor.processChunks(async chunk => {\n    // Process each chunk\n    const results = await Promise.all(\n        chunk.map(item => fetch(`/api/process/${item.id}`))\n    );\n});

","hint":"Think about memory efficiency and how to properly slice arrays into chunks.","dailyQuestion":false,"difficulty":"HARD","customQuestion":false,"slug":"missing-generator-logic-dataset-chunk-processor","slugGenerated":true,"description":null,"title":"Implementing a Generator-based Chunk Iterator for Large Dataset Processing 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":"136bm5n0odp6","question":"What's the correct implementation for this simplified virtual DOM diffing algorithm?","createdAt":"$D2025-01-07T22:03:01.335Z","updatedAt":"$D2025-01-31T22:40:38.455Z","questionDate":"","answerResource":null,"correctAnswer":"136bm5n0odp2","codeSnippet":"$60","hint":"Think about efficient property comparison and handling different types of DOM updates.","dailyQuestion":false,"difficulty":"HARD","customQuestion":false,"slug":"implement-virtual-dom-diffing-algorithm","slugGenerated":true,"description":null,"title":"Implementing a Virtual DOM Diffing Algorithm in JavaScript: Best Practices and Examples","questionType":"MULTIPLE_CHOICE","expectedParams":null,"functionName":null,"returnType":null,"testCases":null,"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false},{"uid":"136bm5n0t82a","question":"What code is missing to implement a memory leak detector that monitors DOM mutations?","createdAt":"$D2025-01-07T22:06:47.310Z","updatedAt":"$D2025-01-31T22:40:38.455Z","questionDate":"","answerResource":null,"correctAnswer":"136bm5n0t826","codeSnippet":"

class MemoryLeakDetector {\n    constructor() {\n        this.nodeMap = new WeakMap();\n        this.detachedNodes = new Set();\n        this.observer = new MutationObserver(this.handleMutations.bind(this));\n    }\n\n    start() {\n        this.observer.observe(document.body, {\n            childList: true,\n            subtree: true\n        });\n    }\n\n    handleMutations(mutations) {\n        mutations.forEach(mutation => {\n            _______________________\n            _______________________\n            _______________________\n        });\n    }\n\n    detectLeaks() {\n        return Array.from(this.detachedNodes)\n            .filter(node => this.isLikelyLeak(node));\n    }\n\n    isLikelyLeak(node) {\n        return !document.contains(node) && \n               this.hasEventListeners(node);\n    }\n}

","hint":"Consider tracking both node removal and reattachment.","dailyQuestion":false,"difficulty":"HARD","customQuestion":false,"slug":"implement-memory-leak-detector-dom-mutations","slugGenerated":true,"description":null,"title":"Implementing DOM Memory Leak Detection with MutationObserver in JavaScript","questionType":"MULTIPLE_CHOICE","expectedParams":null,"functionName":null,"returnType":null,"testCases":null,"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false},{"uid":"136bm5n0vhgp","question":"Implement the missing transition logic in this state machine:","createdAt":"$D2025-01-07T22:08:32.805Z","updatedAt":"$D2025-01-31T22:40:38.455Z","questionDate":"","answerResource":null,"correctAnswer":"136bm5n0vhgl","codeSnippet":"

class StateMachine {\n    constructor(initialState, transitions) {\n        this.currentState = initialState;\n        this.transitions = transitions;\n        this.history = [];\n        this.subscribers = new Set();\n    }\n\n    transition(event, payload = {}) {\n        const currentTransitions = this.transitions[this.currentState];\n        _______________________\n        _______________________\n        _______________________\n        _______________________\n    }\n\n    subscribe(callback) {\n        this.subscribers.add(callback);\n        return () => this.subscribers.delete(callback);\n    }\n}\n\nconst machine = new StateMachine('idle', {\n    idle: {\n        START: { target: 'running', action: () => console.log('Starting...') },\n        ERROR: { target: 'error' }\n    },\n    running: {\n        PAUSE: { target: 'paused' },\n        COMPLETE: { target: 'completed' },\n        ERROR: { target: 'error' }\n    }\n});

","hint":"Consider error handling, history tracking, and subscriber notifications.","dailyQuestion":false,"difficulty":"HARD","customQuestion":false,"slug":"implement-missing-state-machine-transition-logic","slugGenerated":true,"description":null,"title":"Implementing State Transitions in JavaScript State Machine with Event Handling","questionType":"MULTIPLE_CHOICE","expectedParams":null,"functionName":null,"returnType":null,"testCases":null,"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false},{"uid":"15lqm7fczhbb","question":"Sum Values of Object Properties","createdAt":"$D2025-02-21T22:44:49.897Z","updatedAt":"$D2025-02-21T22:44:49.897Z","questionDate":"","answerResource":null,"correctAnswer":"-","codeSnippet":"/**\n * Checks if an object contains all the required properties.\n * \n * @param {Object} obj - The object to check.\n * @param {Array} requiredProps - An array of property names to check for.\n * @returns {boolean} - Returns true if the object has all required properties, otherwise false.\n */\nfunction hasAllProperties(obj, requiredProps) {\n // Your code here\n}","hint":"- Use a loop or a method like Object.values() to iterate over the object's values. \n- Check if each value is a number using typeof or Number.isFinite(). \n- Accumulate the sum of numeric values in a variable.","dailyQuestion":false,"difficulty":"EASY","customQuestion":false,"slug":"check-object-has-all-properties","slugGenerated":true,"description":"$61","title":"Sum Values of Object Properties","questionType":"CODING_CHALLENGE","expectedParams":null,"functionName":null,"returnType":null,"testCases":[{"input":[{"age":25,"name":"Alice"},["name","age"]],"expected":true},{"input":[{"name":"Bob"},["name","age"]],"expected":false},{"input":[{},["name"]],"expected":false},{"input":[{"title":"Manager","salary":50000,"department":"HR"},["title","department"]],"expected":true},{"input":[{"a":1,"b":2,"c":3},["a","b","c","d"]],"expected":false},{"input":[{"x":10,"y":20},[]],"expected":true}],"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false},{"uid":"15pum6m4vmn8","question":"Working with Nested Objects in JavaScript","createdAt":"$D2025-02-01T11:52:34.149Z","updatedAt":"$D2025-02-01T11:52:34.149Z","questionDate":"","answerResource":null,"correctAnswer":"-","codeSnippet":"/** \n * @param {object} person - A person object with `name`, `age`, and `address` properties. \n * @returns {string} - A string describing the person's details. \n */ \nfunction getPersonDetails(person) { \n // Your code goes here \n}","hint":"const city = person.address.city; ","dailyQuestion":false,"difficulty":"EASY","customQuestion":false,"slug":"nested-objects-in-javascript","slugGenerated":true,"description":"$62","title":"Working with Nested Objects in JavaScript","questionType":"CODING_CHALLENGE","expectedParams":null,"functionName":null,"returnType":null,"testCases":[{"input":[{"age":25,"name":"Alice","address":{"city":"New York","zipCode":"10001"}}],"expected":"Alice is 25 years old and lives in New York."},{"input":[{"age":40,"name":"Bob","address":{"city":"San Francisco","zipCode":"94105"}}],"expected":"Bob is 40 years old and lives in San Francisco."},{"input":[{"age":18,"name":"Charlie","address":{"city":"Chicago","zipCode":"60601"}}],"expected":"Charlie is 18 years old and lives in Chicago."}],"nextQuestionSlug":null,"previousQuestionSlug":null,"isPremiumQuestion":false}]