Question 1

What is tsconfig.json and which options matter most?

Accepted Answer

**Target Audience:** Beginners who have just run `tsc --init` and are staring at a wall of options.
**Difficulty:** Easy
**TypeScript version:** All compiler runs below used TypeScript 5.4.5; changes in later releases (5.9, 6.0) are cited from their release coverage and were not run here.

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Every emitted file and compiler mess

Question 2

How do you debug type-resolution and ESM/CJS mismatches with `traceResolution` and `explain`?

Accepted Answer

**Target Audience:** Developers fighting "Cannot find module", TS1479 or types that compile but crash at run time, and anyone asked how they would debug module resolution.
**Difficulty:** Medium
**TypeScript version:** Every trace, explanation and error below came from TypeScript 5.4.5 and Node.js 22 on scratch projects (paths shortened to `/work/...`). `--explainFiles` arrived in TypeScript 4.2 ([Visual Studio Magazine on TypeScript 4.2](https://visualstudiomagazine.com/articles/2021/02/24/type

Question 3

When should you use `moduleResolution: "bundler"` versus `"nodenext"`?

Accepted Answer

**Target Audience:** Developers choosing compiler options for a new app, Node service or library, and anyone who has seen "Relative import paths need explicit file extensions" and wondered why.
**Difficulty:** Medium
**TypeScript version:** Every compiler message, trace and run result below came from TypeScript 5.4.5 and Node.js 22 on scratch projects. `node16` and `nodenext` arrived in TypeScript 4.7 ([Announcing TypeScript 4.7](https://devblogs.microsoft.com/typescript/announcing-typescript-4-

Question 4

How does `allowImportingTsExtensions` work with `moduleResolution: "bundler"` and `.ts` imports?

Accepted Answer

**Target Audience:** Developers using Vite, Bun, Deno or Node's built-in TypeScript support who want to write the real file name in imports, and anyone puzzled by TS5096.
**Difficulty:** Medium
**TypeScript version:** Compiler messages and output below came from TypeScript 5.4.5 and Node.js 22.22 on a scratch project. `allowImportingTsExtensions` arrived in TypeScript 5.0 alongside `moduleResolution: "bundler"` ([TypeScript 5.0 RC announcement](https://devblogs.microsoft.com/typescript/announcin

TYPESCRIPTDECODED.

Easy

What is tsconfig.json and which options matter most?

Medium

How do you debug type-resolution and ESM/CJS mismatches with `traceResolution` and `explain`?

When should you use `moduleResolution: "bundler"` versus `"nodenext"`?

How does `allowImportingTsExtensions` work with `moduleResolution: "bundler"` and `.ts` imports?