TypeScript Data Analysis & Reporting 3

Question 1

You need to type a generic sorting function for report rows that works on any object with at least one numeric field. Which TypeScript constraint achieves this?

Accepted Answer

Answer

Record<string, number> constrains T to objects whose values are all numbers, ensuring the sorting function can safely compare any field.

Question 2

In a TypeScript reporting app, what is the purpose of using 'as const' on a tuple of column names?

Accepted Answer

It narrows types to literal values, enabling safer indexed access

Answer

as const preserves string literal types in tuples, allowing TypeScript to enforce that only valid column names are used as indexes.

Question 3

Which approach correctly types an async function that fetches paginated report data and handles both success and error states?

Accepted Answer

Promise<ReportPage> with try/catch returning typed errors

Answer

A Promise<ReportPage> return type with try/catch allows callers to handle typed success data while errors are caught and handled explicitly.

Question 4

A data analyst asks you to create a TypeScript type for a metric that can be either a raw number or a formatted string percentage. What is the correct type?

Accepted Answer

MetricValue = { raw: number; formatted: string }

Answer

A discriminated object type with both raw and formatted fields keeps both representations together and avoids unsafe union coercions.

Question 5

When using Array.prototype.reduce() in TypeScript to build a frequency map from an events array, what is the correct way to type the accumulator?

Accepted Answer

Provide an explicit generic type argument: reduce>(..., {})

Answer

Providing an explicit generic to reduce tells TypeScript the accumulator's shape from the start, preventing implicit any on the accumulated object.

TypeScript Practice Test

TypeScript Practice Test

TypeScript Data Analysis & Reporting 3