Question 1

What is the role of `react-dom`?

Accepted Answer

**Target Audience:** Frontend engineers preparing for React interviews — assumes basic familiarity with components. **Difficulty:** Easy to Medium > **How to read this doc:** Every concept is explained in plain language first. Right after, you will see a callout like 📌 Interview term: — that is the exact vocabulary a senior engineer would use for the same idea. Every package-export and behavioural claim below was produced by actually running React 19.2.8 in this repo, not describe

Question 2

What is the purpose of the `key` prop when rendering lists in React?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes rendering lists. **Difficulty:** Easy to Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The mismatch in section 3 was produced by typing into a real input and then reordering the list on React 19.2.8. ## 1. Why This Even Matters — A Story First A cloakroom numbers its hooks rather than its coats. Hook 1, hook 2, hook 3. It works perfectl

Question 3

What are the advantages of using React over plain JavaScript?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes JavaScript and DOM basics. **Difficulty:** Easy to Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This is a trade-off question, so the answer below deliberately includes the costs — an interviewer is often testing whether you can argue against your own tool. ## 1. Why This Even Matters — A Story First Picture a whiteboard tracking a foot

Question 4

What is the Virtual DOM in React?

Accepted Answer

**Target Audience:** Anyone preparing for a React interview — assumes basic components. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The reconciliation behaviour in section 5 was produced by actually swapping an element type on React 19.2.8 and observing what happened to the child state. ## 1. Why This Even Matters — A Story First An architect wants three changes to a building. They do not de

Question 5

What is React and its main features?

Accepted Answer

**Target Audience:** Anyone preparing for a React interview — assumes no prior React knowledge. **Difficulty:** Easy > **How to read this doc:** Every concept is explained in plain language first. Right after, you will see a callout like 📌 Interview term: — the exact vocabulary an interviewer expects. The object-shape claims below were produced by running React 19.2.8 in this repo. ## 1. Why This Even Matters — A Story First Imagine decorating a room by giving instructions over

Question 6

Explain the concept of reconciliation in React.

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes rendering basics. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every behaviour below was **executed against React 19.2.8**, including the misassigned checkbox in section 5 — raw output included. ## 1. Why This Even Matters — A Story First A theatre reuses its cast between two performances of the same play. The sensible

Question 7

How can the `key` prop be used to deliberately reset component state?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes reconciliation. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The state and lifecycle transitions in section 3 were **executed against React 19.2.8**. ## 1. Why This Even Matters — A Story First A hotel room is cleaned between guests. Nob

Question 8

How does React Fiber work?

Accepted Answer

**Target Audience:** Engineers preparing for senior React interviews — assumes reconciliation basics. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Sections 3 and 5 are **actual fiber nodes read out of a running React 19.2.8 tree** — React stores one on every DOM element it creates, and this doc walks it. Related:

REACT.JSDECODED.

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