npm install

npm run start

npm run test

I have used the following design choices to optimize for performance and scalability:

1. Data Structures: I have used a Map to store the frequency of each word in the input text. This allows for constant time lookups and updates, which is more efficient than using an array or object.

2. Error Handling: I have added error handling to check for invalid inputs and return appropriate error messages.

3. Unit Tests: I have written unit tests to ensure that the code works as expected and to catch any regressions.

4. Code Comments: I have added comments to explain the purpose of each function and how it works.

5. Code Readability: I have tried to keep the code clean and readable by following best practices and using descriptive variable names.

6. Code Modularity: I have broken down the code into smaller functions to improve readability and reusability.

7. Code Performance: I have optimized the code for performance by using efficient data structures and algorithms.

8. Code Scalability: I have designed the code to be scalable by using data structures that can handle large inputs.

1. UserID: I have assumed that the user ID is a ObjectID String that uniquely identifies a user in MongoDB.