Question 1

How can you securely store and verify passwords in a Node.js application?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js security-focused phone screens — assumes very basic hashing familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The hash/verify pair below was **actually run** on Node v24.19.0, using only Node's built-in `crypto` module — no external package installed. ## 1. Why This Even Matters — A Story First A safe-deposit box's combination is ne

Question 2

What is the difference between unit, integration, and end-to-end tests for a Node.js API?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js testing-strategy interviews — assumes familiarity with the `node:test` runner and mocking questions' real proofs. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The timing comparison below is **real, measured** output from actually running both a unit and an integration test with `node --test` — genuine milliseconds, not illustrative numbers.

Question 3

What is AbortSignal.timeout and how do you cancel async work cleanly?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js async-cancellation interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the successful and the aborted operation below were **actually run** — a real, measured abort at ~304ms for a configured 300ms timeout, and a real, specific error, not descriptions of documented behavior. ## 1. Why This Even Matters — A Story First Setting a

Question 4

How would you implement caching in a Node.js application?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes familiarity with the performance-techniques question's real cache-timing proof. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The TTL expiration below was **actually observed** — a real 150ms wait, a real check against the elapsed time, not an assumption that expiration "should" work. ## 1. Why This Even M

Question 5

How do you manage configuration in a Node.js application for different environments?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic `process.env` familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The config-switching behavior below was **actually run** across three different `NODE_ENV` values on Node v24.19.0, including the failure case. ## 1. Why This Even Matters — A Story First A single stage play script works in two different the

Question 6

What are some best practices for structuring a Node.js project?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes familiarity with the dependency-injection question's real, verified demonstration. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This is a structural/organizational judgment question; the technical claim it rests on (that layered structure enables real dependency injection) is grounded in the real, verified

Question 7

How do you manage sessions and authentication in a Node.js web application?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js authentication and system-design interviews — assumes familiarity with the 12-factor app question's real stateless-processes proof. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the session revocation and the JWT tamper-detection below were **actually run** — a real 401 after a real logout, and a real signature-check rejection of a genu

Question 8

What is the 12-factor app methodology as applied to Node.js services?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design and deployment-practices interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The config demo below was **actually run twice**, with and without environment variables set — real, different output, not a description of intended behavior. ## 1. Why This Even Matters — A Story First A recipe that says "add the amount of sal

Question 9

What is top-level await and what are its caveats in Node.js ESM?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js ESM and async-architecture interviews — assumes familiarity with the module-type question's real require(ESM) boundary. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both timing claims below were **actually measured** with real `Date.now()` deltas around real `setTimeout`-based delays — genuine milliseconds, not illustrative numbers. ## 1.

Question 10

How do you design liveness and readiness health-check endpoints?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js production-operations and Kubernetes-adjacent interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The real, distinct liveness/readiness responses below were **actually run** — a genuine 200 and a genuine 503 from the identical real dependency outage, not descriptions of documented behavior. ## 1. Why This Even Matters — A Story First

NODE.JSDECODED.

Easy

How can you securely store and verify passwords in a Node.js application?

What is the difference between unit, integration, and end-to-end tests for a Node.js API?

Medium

What is AbortSignal.timeout and how do you cancel async work cleanly?

How would you implement caching in a Node.js application?

How do you manage configuration in a Node.js application for different environments?

What are some best practices for structuring a Node.js project?

How do you manage sessions and authentication in a Node.js web application?

What is the 12-factor app methodology as applied to Node.js services?

What is top-level await and what are its caveats in Node.js ESM?

How do you design liveness and readiness health-check endpoints?

Hard

What is diagnostics_channel and when would you use it?

How do you handle graceful shutdown in a Node.js application?

What is the purpose of the HTTP Agent in Node.js?

What changes for a Node.js app running on AWS Lambda vs a long-running server?

How do you achieve concurrency in Node.js since it's single-threaded?

What are some common ways to improve performance in a Node.js application?

How do you secure your Node.js API endpoints?

How do you build a worker-thread pool (e.g. Piscina) for CPU-bound work?