TypeScript Data Analysis & Reporting 2 — Questions and Answers
Question 1: Which TypeScript utility type transforms all properties of an interface to be read-only, useful for immutable report data structures?
- Partial<T>
- Readonly<T> (Correct answer)
- Required<T>
- Mutable<T>
Correct answer: Readonly<T>
Readonly<T> makes all properties of type T read-only, preventing accidental mutation of report data.
Question 2: In TypeScript, what is the best way to type a function that aggregates an array of sales records and returns a summary object with total and average?
- Use 'any' return type for flexibility
- Define an explicit return type interface like SalesSummary (Correct answer)
- Use unknown return type
- Return a tuple instead of an object
Correct answer: Define an explicit return type interface like SalesSummary
Defining an explicit return type interface ensures the aggregation function always returns a predictable, well-typed summary object.
Question 3: When building a TypeScript data pipeline, which pattern allows you to chain multiple transformation steps on a dataset while preserving type safety?
- Using 'as any' between each step
- Method chaining with generic functions that preserve input/output types (Correct answer)
- Casting to unknown between transformations
- Using JavaScript's loose equality for comparisons
Correct answer: Method chaining with generic functions that preserve input/output types
Generic functions that accept and return typed data allow method chaining while TypeScript infers the correct type at each step.
Question 4: What TypeScript feature would you use to create a type that maps each key of a report schema to a formatter function for that field's value?
- Conditional types
- Mapped types (Correct answer)
- Template literal types
- Intersection types
Correct answer: Mapped types
Mapped types iterate over an existing type's keys and assign a new type to each, perfect for creating per-field formatter maps.
Question 5: A TypeScript function receives raw CSV data as a string and must return typed row objects. Which approach is most type-safe?
- Parse and cast with 'as unknown as T'
- Return Record<string, string> and cast later
- Use a generic parser with a validation schema that returns T | null (Correct answer)
- Use eval() for dynamic property access
Correct answer: Use a generic parser with a validation schema that returns T | null
A generic parser with runtime validation returns T when parsing succeeds or null on failure, maintaining type safety through the boundary.
Question 6: When typing a pivot table operation in TypeScript, which structure best represents a result where row keys and column keys are both dynamic?
- Map<string, Map<string, number>> (Correct answer)
- Array<Array<number>>
- Record<string, number>
- Set<string>
Correct answer: Map<string, Map<string, number>>
Map<string, Map<string, number>> naturally models a two-dimensional pivot where both axes have string keys and values are numeric.
Question 7: Which TypeScript compiler option should be enabled to catch implicit 'any' types that can silently corrupt data analysis results?
- strict: false
- noImplicitAny: true (Correct answer)
- skipLibCheck: true
- allowJs: true
Correct answer: noImplicitAny: true
noImplicitAny forces every variable and parameter to have an explicit or inferred type, preventing silent 'any' from hiding type errors in data pipelines.
TypeScript Data Analysis & Reporting 2
Which TypeScript utility type transforms all properties of an interface to be read-only, useful for immutable report data structures?