Trainee Engineer

1. What is a variable, and what are the differences between different types of variables (e.g., var, let, const) in JavaScript?
2. How can you update state in React by using a callback function?
3. What is useCallback? How does it work internally, when should you use it, when should you avoid it, and can you give an example?
4. What is useMemo? How does it work internally, when should you use it, when should you avoid it, and can you give an example?
5. What is useEffect? How can we handle side effects in React using useEffect — with a dependency array, without a dependency array, and with an empty dependency array?

You are given an array of integers ranging from 1 to n. The numbers are in random order, and exactly one number is missing in the sequence. Write a function to find the missing number without sorting the array.

Example:
Input: [3, 7, 1, 2, 8, 4, 5]
Output: 6

1. Normal Variables vs State: What is a normal variable and how is it different from state in React?
2. Updating State with Callback: How can you update state using a callback function?
3. useCallback: How does useCallback work internally? When should you use it and when not? Can you give an example?
4. useMemo: How does useMemo work internally? When should you use it and when not? Can you give an example?
5. useEffect: How can you handle side effects in React using useEffect? Explain with dependency array, without dependency array, and with an empty dependency array.
6. Key in React: How do keys work in React? Why are they important, and where should you use them?
7. FlatList: How does FlatList work? Explain key props, inverted FlatList, and data manipulation.
8. ScrollView: How does ScrollView work? When should you use it over FlatList?
9. View and Text: Explain layout using Flexbox in React Native. Discuss default direction, justifyContent, alignItems, etc.