Coding Questions
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You need to implement a type-safe event emitter that supports wildcard listeners. Which implementation correctly handles all the edge cases?
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JavascriptEventsPatterns+2
Medium
You're implementing a shopping cart using React's useReducer. Which implementation correctly handles adding items while preventing duplicates and updating quantities?
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ReactUsereducerReact hooks+4
Medium
You are optimizing a React app with multiple child components that receive the same prop. What should you use to avoid unnecessary re-renders?
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ReactOptimizationReact hooks
Easy
Complete the missing code to transform an array of user records into a structured report:
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ArraysReduceMap+1
Medium
Complete the missing code to make this controlled form component work:
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ReactFormsControlled components+3
Easy
When building a music streaming app, you notice user actions (like seeking in a track) are causing too many API calls. How would you optimize the custom hook below to reduce server load while maintaining a smooth user experience?
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ReactReact hooksDebounce+3
Medium
You are trying to create a while loop that will increase the petCount to 5. Why is this solution not working?
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JavascriptLoopsWhile loop+3
Beginner
You need to implement a custom React context for managing theme preferences. Which implementation correctly handles dynamic theme updates?
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ReactReact contextTheme+2
Medium
You're building a custom virtualized table component for large datasets. What's the issue with this implementation?
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ReactReact hooksVirtualization+2
Medium
What will this code output?
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PromisesError handlingAsync
Medium
You're implementing an infinite scroll feature with data caching. What needs to be fixed?
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ReactReact hooksInfinite scroll+3
Medium
You're building a search bar component that needs to suggest results as the user types. The component should minimize API calls and handle race conditions. What's missing in this implementation?
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ReactDebounceFetch+1
Hard
Fill in the missing code to create a custom React hook that manages form validation with dynamic rules:
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ReactReact hooksForm validation+2
Medium
You're implementing a simple Observable pattern with operators. What's the correct implementation of the pipe method?
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JavascriptObservablesOperators+2
Medium
In a React application, you're debugging a complex asynchronous operation where multiple events are being handled. What will be logged to the console in the following code?
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ReactEvent loopAsync+4
Hard