TypeScript Data Analysis & Reporting 2

Question 1

Which TypeScript utility type transforms all properties of an interface to be read-only, useful for immutable report data structures?

Accepted Answer

Readonly<T>

Answer

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?

Accepted Answer

Define an explicit return type interface like SalesSummary

Answer

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?

Accepted Answer

Method chaining with generic functions that preserve input/output types

Answer

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?

Accepted Answer

Mapped types

Answer

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?

Accepted Answer

Use a generic parser with a validation schema that returns T | null

Answer

A generic parser with runtime validation returns T when parsing succeeds or null on failure, maintaining type safety through the boundary.

TypeScript Practice Test