TypeScript Data Analysis & Reporting 5

Question 1

In TypeScript, how would you type a generic data filter function that takes a predicate and returns only the matching elements with the correct narrowed type?

Accepted Answer

function filter<T, U extends T>(arr: T[], pred: (item: T) => item is U): U[]

Answer

Using a type predicate '(item: T) => item is U' causes the returned array to be typed as U[], reflecting the narrowed type after filtering.

Question 2

A report dashboard needs to display data from three different API endpoints with different shapes. Which TypeScript pattern helps you normalize them into a single unified type?

Accepted Answer

Define a union type and use type guards to normalize each shape into a common interface

Answer

A union type with type guards allows TypeScript to understand each variant's shape so you can safely extract and normalize fields into the common interface.

Question 3

What does the TypeScript 'infer' keyword enable when used in conditional types for data analysis utilities?

Accepted Answer

It extracts and names a type from within another type during conditional type evaluation

Answer

The 'infer' keyword captures a type variable during pattern matching within conditional types, allowing utilities like ReturnType<T> to extract inner types.

Question 4

You need to deep-freeze a report configuration object at runtime and reflect that immutability in the TypeScript type. Which approach achieves both goals?

Accepted Answer

Use Object.freeze() and type the return as DeepReadonly<Config>

Answer

Object.freeze() prevents runtime mutations while DeepReadonly<Config> (a recursive mapped type) reflects that immutability at the type level for nested objects.

Question 5

When integrating a third-party charting library with no TypeScript definitions, what is the safest way to type its data input in your TypeScript data layer?

Accepted Answer

Write a custom .d.ts file with at least the input shape you use, or use DefinitelyTyped

Answer

Writing a minimal .d.ts declaration for the portion of the library you use provides type safety at the integration boundary without requiring a full type definition.

TypeScript Practice Test

TypeScript Practice Test

TypeScript Data Analysis & Reporting 5